Shoebox issues???

I'm having a couple of different troubles with my shoebox compressor. It's an older chain drive model and I am the second owner.

First, it stopped filling at 2500psi but kept running. I used sudsy water to find air leaking at the bottom of the big aluminum air block. Don't know what to do to address this issue nor what parts I'll need. Could you please advise me? The air is bubbling at what looks like the very bottom of the block where it rests on the inside of the red housing.

Second, the previous owner used Penn fishing reel grease on his last filling session because he had misplaced his white lithium grease. Said he dabbed it every hour with a little on the end of his finger to each piston shaft. When I initially tested the machine, we hooked my tank up to the shoebox, let it run and fill a while. After turning off both compressors, depressurizing the tank fill line, the air inside the Porter Cable pancake compressor pushed through the system somehow and into the tank line before we were able to get it all unhooked.

Before we unhooked the foster fitting from the shoebox, the air pushing through the system from the pancake, also pushed some grease out of the shoeboxs' fill nipple. I know this to be true because after we unhooked the Foster fitting and while the pancake was still hooked up, I noticed a little bit of that green Penn reel Grease the guy used before me was coming out of the shoe boxes fill nipple and sticking to the edge of the hole around the nipple as the air from the pancakes resorvoir dumped it's air. I wiped at it to see what it was and sure enough, grease!

I immediately became concerned that grease might have gotten into the tank itself during the test fill. I opened the tank to dump about 300psi to try and at least purge the fill line and sure enough, little tink bits of grease in the line. Don't know if it got in the tank itself or not as I can't see inside the tank. Also don't know if or how this will affect filling my guns so before I did, I wanted to take the time ask you your advice.

This machine did not come to me with a vent stop and now I see that it is definitely supposed to have one. Could this be why the air pushed back through the system from the pancake or do you think the leak at the bottom of the air block could be the culprit. I definitely understand that I probably hooked it up and unhooked it incorrectly and out of order and won't do that again but the other issues are really what I need help with.