Eagle Starter Problem

I'm having a problem with my '95 Eagle's starter (Vision ESI 3.3; ND
starter). Any time it's damp out (it seems) the starter solenoid will
simply click and not engage the starter, or simply give a little half
hearted crank. I took it out last week and had it tested. It didn't
turn up any problems, and I had they key it 15 or 20 times to make sure
it didn't show up any issues. The Pep Boys tech who bench tested it
mentioned he's had the same issue with his late 90's Intrepid, which
likely has the same starter in it. He didn't come to a resolution
either.

While I had the starter out, I disassembled the solenoid and took the
contacts out of it and cleaned them up They weren't horrifically
corroded or anything, but I figured bare clean metal would get e better
connection.

I'm still having the same problem, and I'd like to try and resolve it
before cold weather sets in. I'm thinking the next thing I'll do is
replace the cables. I dont' think my battery is bad, because I just
replaced it last fall, but I might have it load tested to rule that
out.

What's next? I see some notes on the solenoid contacts... Is there a
way to know for sure whether the contacts are actually bad?