Anyone have any knowledge of what this part is and where i can get one. It does not show up as an individual part number in the montesa parts manual, and is next to the rebound spring on the seat pipe in the left hand fork. Not sure if its a bump rubber or a seal as the old one is unsalvageable.  

Looks like a top out spring with a glorified washer.  Basically it would be quieter than something harder when pulled into the top out position but obviously it isn't durable enough to hold up.  You could try some PVC cut to fit.  It's thickness isn't horribly critical, it just keeps the spring end from cutting up whatever it's hitting essentially.