Having Hydraulic Issues With My LM4

[Solomon]

    I'd like to pick everybody's brain.    I lack any workable knowledge of hydraulics and I'm having some issues with about 6 of the cylinders on my mill.  They extend fine but do not retract.   I could tie the lever down and go out for breakfast bofore they fully retract.
  Could this be a problem in the valve stack ?
A couple of times the stems on the valves got weathered and were sticking and I used PB blaster to free them up.   Did I commit a big no no there and melt some O rings in the valves ?   Just give you the straight info. 
Can someone give me an Idea where to start looking for the problem ?   What to check first ?
Pete ,   Chesapeake, Virginia :P

[boscojmb]

Hi,
Assuming that the other 4 cylinders on your mill are working properly, it's very unlikely that the pump is an issue.
I take it that you have checked the obvious ( leaks, full of fluid, Ect.).

It sounds like a valve issue to me.
The seals at the front of the valve spools are just dust seals. I doubt the PB Blaster damaged anything internal.

I would take the valve stack apart, remove the spools, and clean everything.
Did anyone use teflon tape anywhere in your hydraulic system? Teflon tape will drive you nuts if it gets into your hydraulic circut.

I was at the Logmaster shop a few years ago. When I was there they where working on a mill identical to yours, same symptoms.
The problem ended up being something stuck in the valves.