[s-cars] 1993 UR S4 Won't Start

[Szarka Strubachincoscow]

Hi all:

New subscriber to the S-Cars list, but a long-time Audi owner. 
Patient is my '93 UR S4 with 91K miles, MTM stage 1.

Problems started with the classic bad ignition switch symptoms; i.e.
the grinding noise from the rear of the engine followed by the flipped
out temp display, radio, etc that you get when the power reduction
relay is still closed.  After a short time I discovered that turning
the key in the ignition back about 2 mm's would cause the starter
motor to disengage and the grinding would stop.  I drove the car this
way for about two weeks using the "turn the key back a bit" method to
avoid the grinding and, hopefully, damage.

Took the car on a 600-mile round trip during which she ran fine. 
After sitting in the garage for two days after the trip I went out to
start her up and no go.  So, I removed the IC and replaced the
ignition switch (electrical part of it).  The switch was cracked and
certainly needed replacing.  Tried to start her again—still no go. 
The engine turns over and I can see the timing belt, alternator belt,
etc turning, but the starter doesn't sound quite right.  I confirmed
last night that I have spark to each plug and also have fuel as the
plugs are wet and I can smell it.  I don't think I lost a tooth on the
flywheel or else how could I not have had problems on the 600-mile
trip?

Cleaned battery connections, chassis ground under the seat, etc.  No joy.

So what do you all think?  Starter motor?  Solenoid?  Typically I
would not expect the engine to be turning over at all if I had a bad
starter, but I know a lot more about Type 44 cars, so perhaps this
happens with an S4??  Grasping at straws now!  Any opinions or BTDT
greatly appreciated.

Thanks,

--Sz