This was the ofending part: The switch that didn't clamp well.
I have another Canon 35mm f/2.0 Prime lens that the focus ring didn't work as well. Dismantled the whole thing also.
It seems that it has the internal spining mechanism broken. I bought it refurbished in the US and I still have the warranty but it's too much hassle having it sent there, paying shipping and waiting for weeks to have it fixed, so just went ahead and took care of business myself. The guy sure seems to know what he's doing. Gotta pick it tomorrow though.
I just hope the Nikon lens doesn't become broken again and this time its fixed for good.