This is a repost - my original post seems to have gotten lost somewhere. Can anyone help me with this?

My starter won't start on my '86 744.

Just spent two and a half hours in 33 degree cold on a very dark night cleaning all contacts (battery, starter solenoid) and it started right up - starter sounded more peppy than I can remember it ever sounding! I have noticed for a few months now that the starter has been sounding tired, the way it does when it is 10 degrees F outside. I would venture to guess that the contacts were corroded and the starter wasn't getting enough juice. The two or three times it started up after I cleaned the contacts, it started with great enthusiasm!

But, alas,then it returned to its previous behavior - turn ignition switch, "click" (one), lights go out, no turn over of engine. Then the solenoid stopped clicking at all (it always clicked before when it wouldn't turn over). All I hear now is the clicking of a relay. Lights (headlights) still go out, indicator lights all go on on the dash, but no action from the starter. I find that if I fiddle with the thin green wire it makes the solenoid click again but it never turns over now. And then it stops clicking again.

I have been warned not to assume the starter itself is at fault (lots in FAQ about checking electrical connections) but am wondering what people's experience with starter problems has been. I have ordered a rebuilt Bosch starter from FCP Groton in hopes that replacing it will solve the problem. What challenges do I face in replacing the starter? (The FAQ's make it sound a little scary.)
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Darius in Albany NY '86 744 GLE (174K); '91 745 Turbo (164K)