 You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
  You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
Just looking at my XTR 11s mecb while changing a tyre, and noticed the lower jockey wheel has maybe had its' day. The teeth are all worn to a point. Which got me thinking.... that mech - and those jockeys - are on their third bike, I originally bought them as an upgrade for my 26er Nicolai Ion, so that mech has been on the go side about 2013. It still shifts perfectly,
Starting to think this xtr stuff might be worth the extra few quid.
Smashed the carbon cage of my 2 month old XTR mech by hitting a stick at the side of the trail. Never broken or even bent a mech in many years riding.
Replaced it with an XT mech with aluminium cage. Never missed a beat for 7 years after that. Now sold the bike on. 
Shimano stuff seems pretty good but why go XTR when XT is just as good without the fancy weaknesses.
And three bikes before replacing the jockeys!! Wow. I usually find 1 season is all you get before the bearings seize. Then another 6 months before changing the remaining spur for a new wheel with real teeth.
IME jockey wheel life is dictated by soil type. Where I lived near Edinburgh, jockey wheels lasted forever. Here in the Cairngorms they're an annual consumable.
Never had a mech but all my bikes (except the fatbike, which can't) have M970 XTR cranks on, came out in 2006 and still going strong, and barely any heavier than the carbon cranks I bought to try and replace them that both broke. Pain in the arse to remove, mind.
IME jockey wheel life is dictated by soil type. Where I lived near Edinburgh, jockey wheels lasted forever. Here in the Cairngorms they’re an annual consumable.
Absolutely! Same with the other thread about frame bearings - lifetime will absolutely be determined by usage. Yorkshire seems to also be "a bit trying" on bike drivetrain components.
My XTR M9000 groupset lasted about 2,500 miles of Yorkshire filth, including a few chain swaps. I went through two sets of jockey wheels pretty rapidly, before swapping to Hope and accepting the characteristic clatter as a price worth paying for not having to change them every few months. They lasted well! Otherwise, the rest of the groupset survived pretty well until a combination of needing chainrings, cassette and probably a new mech, as well as a desire to move to 1x triggered a full replacement.
I looked into replacing with M9100 XTR but the reality was that for the price of a whole 12-speed XT groupset (chainset, mech, shifter, chain, cassette), I could just about buy the XTR crankset...without rings! I couldn't even nearly justify that, so swapped to XT with no regrets.
It's worth noting that XTR has a slightly longer warranty (3 yrs vs 2 yrs) and that I still have the XTR carbon-levered brakes and pedals on the bike because there was nowt wrong with 'em 🙂
No XTR mech but my XTR spec M969 SPDs I bought in around 2000 are still going strong - on my current hardtail.
Smoothest setup I've ever had was on my last bike. 1 x 11 Shimano XTR with a wide range Sunrace cassette.
Just upgraded my mates old B Twin hardtail with some stuff out of my spares box today (11 speed XT mech, SLX shifter and slightly used 11-42 SLX cassette). I was amazed at how nice it felt! Took about 2 minutes to set up perfectly.
I like my GX Eagle, but I reckon Shimano XT/XTR 11 speed with a wide range cassette was better.
I never had any trouble with my XTR mech and I don't think I've ever broken one. Missus managed to twist a GX Eagle when a stick got lodged in it. Didn't shift right after that.
Most of my bikes have ancient 9-speed XTR rear mechs and those seem to last forever.
Having just tonight smashed the carbon cage on my XTR M9100 mech, can anyone tell me if it's possible to buy replacement cages?
To OP's original question... dunno I'm afraid, only been running it a year but jockey wheels good as new.
M970 XTR cranks on, came out in 2006 and still going strong
Ah yes. Great cranks no doubt. In fact, I looked for some just last week to replace my worn-out X01s. They seem to be holding their value a little too well, though.
I have a 10 year old XTR 970 crankset on my SS now. I've been thinking about polishing it up.
I've had two 11spd XTR mechs and both didn't last that long until they went sloppy.
XT have lasted much better.
Other XTR is very good though; shifters, spuds to name two.
Unlike my 2013 xtr cranks that are on their 3rd bike and still going strong. My xtr carbon cage on the other hand , like others have mentioned, only lasted a couple of weeks and disintegrated after touching a twig.
@ robertgray05 yes you can https://www.probikeshop.com/en/gb/shimano-xtr-m9100-sgs-12v-rear-derailleur-long-outer-cage-y3fa98080/167004.html
However for that price it’s cheaper to buy a brand new 12 speed xt mech.
My 2010 Stumpjumper FSR is on its original xtr mech, so it's lasted 10years so far.
The cage took a whack 5years or so ago which cleaved a chunk of the carbon away (like splitting slate). One cage now has a large portion that is only about 50% thickness but it still works fine.
Really smooth shifting too and have hardly eve had to tinker with it. 
Most of my bikes have ancient 9-speed XTR rear mechs and those seem to last forever.
I've got one of the old M950 (battleship grey) 9sp mechs which is about 15 years old and still shifts perfectly. It's had a couple of sets of jockey wheels in that time but otherwise is perfect.
Having just tonight smashed the carbon cage on my XTR M9100 mech, can anyone tell me if it’s possible to buy replacement cages?
Yes:
Part list: 
e.g.  https://www.sjscycles.co.uk/gear-spares/shimano-xtr-rdm9100-inner-plate-sgs-y3fa26000/
(might have to shop around for stock though)