eraser fixed my Siggy 10-20 with only 1 light pass.
I had the same issue that TG has while I was out'n'about where the camera would basically lockup.
Remove lens, refit .. it helped a couple of times, but it was all over the place.
@ home, I did the eraser thing and have never had trouble with the Siggy ever since.
The contact cleaner fixed my Tamron 28-75 issue.
I only used the contact cleaner because I discovered that I had some left over! Otherwise I'd have just used the eraser again.
Contact cleaner sprayed onto a cotton bud so it was wet. cotton bud swiped over contacts on the wet side, then a very light swipe on the dry side, you don't want lint coming off, so just a light drying action. In fact it doesn't really need it, I just did it.
Never had an issue with the Tammy again either.
ps. I'm also going colourblind. I thought that most lens contacts are gold coloured, but are in fact a silvery silver colour, whereas the Sigma's are different using a dark coloured finish.