I also have a 6D and have shot the Super Tak 135/2.5v2. Excellent center sharpness, about F3 is the best balance between good bokeh and controlling the abberation. Bokeh has interesting character at mid-distances, and can produce 'cats-eye' in the balls. Significant magenta and green in the out of focus bokeh wide open.
See
this thread for lots of info on Lens Disassembly. I have CLA's this exact model before but didn't document it. The thinner front ring on this model can make it a little harder to remove compared to it's brothers. The construction is similar to the other mid-tele taks.
Some types of fungus look a bit like lint/paper. If it's very minor, it may not be worth the trouble to CLA.
These
spanner wrenches are very sturdy for the price.