83 300SD Mystery Starting problem

[Oldyella]

My 300 SD had been starting with no problems and yet yesterday when I went to leave work, it would not engage the starter at all. It was in the lower 30's. Battery appears OK, terminals cleaned. Previously, replaced a faulty glowplug after tests. The GP Relay does "clunk" after a few seconds. I tried the trick given in many of the threads of jumpering 1 and 3 on the terminal on passenger side but got only weak spark no solonoid click. Later took the wires off the terminals and cleaned them as the terminals were highly corroded. After that the jumper trick between 1 and 3 resulted in a notable solinoid clunk but starter didn't turn over.

That seems to indicate the starter, but I have had no warning signs of starter dragging or solenoid not working. Is it maybe only the solenoid ??

I will also pull the battery and have it tested but it gave no warning signs either.

Ideas would be appreciated?

Thanks