Aside from the tensioner pulley, did you check the tensioner arm itself? It should pivot smoothly about the crank axis only. Wobble is bad, roughness, clicks or steps when pivoting is bad.

Replacing the AC compressor shouldn't be difficult in a 210 since it's not difficult in a 124. You might have to remove the sway bar which is just a few bolts as long as the front axle is level. If the issue is the pulley or clutch, you should be able to tip the driven end of the compressor downward and work on it without touching the refrigerant charge.

I can't imagine a problem with the PS pump pulley that isn't also causing a front seal leak. Is the back side of the pulley wet or grimy?

Sixto
MB-less