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The 20+ year old Marin Rift Zone shock is moot holding air or ribbing any sort of damping now.
The bike has had a great life and is being put out to grass on commuting duties.
If i could just put a couple of old skool elastoners in the air chamber I'd be happy. Has anyone bodged one of these by injecting expanding foam or epoxy resin into the air chamber or something?
Not done anything like that, but on an old fs a few years back the Fox Alps expired and was unrepairable. I just picked up a cheap secondhand Rockshox shock from eBay for about £50. As long as you’ve got a common shock length you should be able to get something cheap just to get you up and running.
It is actually possible to DIY rebuild these shocks but it requires a lot of care (not least make sure you don't drop the stack of shim/valve disc things). The seal specs are available online if you want to use cheap "off the shelf" industrial ones. There are also kits like https://www.ebay.co.uk/itm/Fox-Float-R-RP2-RP23-RP3-Triad-IMPROVED-Damper-Service-Rebuild-Oil-Seals-Kit/302455118507?hash=item466bbadaab:g:meMAAOSwEWJZvSPU but they're not that cheap.
Obviously only worth attempting if you accept the shock has no value and you might destroy it.
You could use normal air instead of nitrogen.