I got this broken Paslode PowerMaster 5350/90S framing nail gun from a pile of free tools. The sleeve seal and bumper post were hard, cracked, and brittle. I also went ahead and replaced all the O-rings while I was in there. The repair process should be pretty much the same for any 5300 series nailer. See the links below for the parts and tools I used:
Sleeve Seal & O-Ring Kit (PN: 402011 ):
https://www.ebay.com/itm/160960366740
Bumper Post (PN: 500453 ):
https://www.ebay.com/itm/231412921074
Snap Ring Pliers:
https://amzn.to/3eHsQ5l (affiliate*)
*Purchasing from these Amazon affiliate links earns my channel a small commission. Think of it as a tip that doesn't cost you anything. Thanks for the support!