Ok, this one is new to me. 300sdl, 87 w/ 377k and climbing runs great!..but this time would not crank. 40's all day here. Hesitated to crank at noon, but started. Went out at around 3 and would not crank. Car had all warning lights, glow plugs worked..so assumed 3.5yr old battery. Took battery to two parts places and both said probably - shows 12.6 volts. Bought battery and installed; turned key-same thing. Will not crank; no click like solenoid, but all other electrics work. Tried gear in neutral/ back to park (safety switch ???) but no difference. Car is sitting in drive awaiting friendly tow truck. Anyone have any guesses? Possibly starter?..I did notice an-almost-alternator-bearing-whine last few times car was running, right after start. Open to suggestions/ guesses?

love my car and this one is a new one on me.

THX