Hello all - I'm a new owner of a tough old 190D (223k mi. and counting)
and while she seems to be running pretty stable given her age, I've
noticed the alternator/voltage lite glowing faintly at idle, and found
that the main serp. belt is very loose.  I tracked that down to the
tensioner pully sitting fully slack, and after staring at the drawing in
the service manual, said "hey, there should be a spring there."  I don't
know if it wasn't there when I bought it, or it sprung off to other
places recently, but it's gone.  The pulley looks fine, otherwise.  I
can move it with a pliers and tension the belt, which also looks in good
shape.

Not wanting to engage the services of the local Euro auto shop to the
tune of $500 or so, I've since rigged up a field repair involving some
wire and the nearest bolt, but I owe it to the car to do better than
that.  I know the full tensioner assembly is available on ebay or the
parts sites, but since that appears fine (and replacing it would require
me to remove the radiator and refit the belt, a task I don't think I'm
up for,) is it possible to buy just the spring?  Or perhaps the better
question is, what size/tension/strength spring is needed, and does
anyone know of a source for one?

Thanks much, and keep on rollin' to 500k!