Finally had a chance to work on the starter issue. I was planning to run Patrick's voltage drop test so I went to start the car Friday morning and I hear the starter spinning but the engine won't crank
I jacked up that car and check the starter and it was loose. The bolts on the face plate holding it to the bellhousing were tight but the body of the starter was literally a >1/4" loose. I removed it and the two 25 torx screws that hold the starter to the face plate had backed out, and one had completely snapped in half... WTF!!!
I also saw deep grind marks on the inner plate of the starter, and very light wear on the adjacent face of the flywheel (not the teeth). I hand cranked the engine and checked for any damage to the teeth on the fly wheel and thankfully they all look fine. The piņon gear on the starter also looked fine.
I bought a direct replacement (powermaster 9603) and installed it today. Instructions say
"USE BLUE LOCTITE ON TORX 25 SCREWS"... well guess what, there was NO loctite on the screw I removed from the broken starter!! It doesn't come with loctite from the factory and I guess my mechanic didn't add it. took 5000 miles to back out and fail
Ran the car today with the new starter for 25 miles, got the engine hot (190-200F), shut it down for 5-10 min, let it bake under the hood and it started right back up. The new starter cranks much stronger (cold or hot) than the original. I'll monitor it over time, but if it begins to exhibit the same slow crank after it gets hot (like the original) then I assume it's clearly a heat soak issue and the solenoid is wearing over multiple heat cycles?