I drained a bunch of fluid out when I removed the down valve and replaced it with new fluid last night.I would suggest replacing the fluids if you do not know how long is has been inservice just my 2 cents worth
I stuck my finger in the hole where the spring and ball were and tried to feel for burs or debris and didn't notice anything. I'm not sure that is the official inspection method. I then stuck a paper towel in there and twisted it around a bit before re-assembly.were you able to check the ball seat?
About an hour after I put things back together it seemed like it moved a 1/4" or so. Didn't seem like a good sign. I just checked it now, about 15 hours later and it has moved about 1/2" total. If it just moved about a 1/2" per day, that would be fine by me. I am going to create a story stick to track it's movement over time.