Not personal experience of this but if that is the 135mm f2.8 you got a bargain.......based on clean looking examples for sale online.
Though it's apparent condition looks dire with that ding/dent on the front end.
Two thoughts occur to me:-
Is it free of fungus.....if not I would never use such a lens.
The damage suggests a significant drop onto a hard surface, so does the focus ring turn smoothly and does the aperture ring turn & does the lens 'stopdown' i.e. can you see the diaphragm 'follow the ring settings'???