Chainsaw Repair

My wife bought me this 5000 for Christmas 40 years ago. It ran great for 15 years but started having trouble so I got a 346XP, then a Redmax 353. I love all these saws and would like to keep them all running. The 5000 cuts well except that I can't get the oiler to pump up to the port for the bar. I put a pump on it many years back and the worm gear and splines look ok. I just put a new inner bar plate on but have never replaced the oil lines. I have a used upper one on order(parts aren't easy to find!). The lower one doesn't have anything obviously wrong unless there's a filter or check valve thats supposed to go in the coil spring on the bottom. I'm sure it's brittle though.

It must be pumping because oil drools out the bottom of the bar plate. The upper hose looks like it may have broken off where it necks down. I'll replace it when the other one gets here.

I'm confused about the little pin (.050"-.060") that goes into the case along the pump cylinder. I had replaced it with a cotter pin though I can't remember doing it.
What the heck does it do and what dimensions should a replacement be?