My old beloved Minolta G 28-70 started doing tricks on me as the aperture started to get sticky. I called several repair shops in France where I live who basically told me to buy a new Zeiss because spare parts couldn't be found for this 1993 built lens... At the Photo show in Paris earlier this year someone told me I should continue searching for a repair center as in good shape, this lens can fetch up to €600 in Paris and a new Zeiss is, well, expensive.
After numerous attempts I found someone in Paris who did the job and I must say that over 250 shots later, the results are spectacular; I had forgotten what great lens Minolta made and mounted on a A99 it is terrific, albeit autofocus slow. Not an inexpensive repair, but I am a happy person!
So if you have problems with those old G lens, don't despair, someone can surely help you out there...
All shots in these two albums made witht he 28-70 G Minolta:
https://www.flickr.com/photos/marcpecquet/sets/72157652388647645/
https://www.flickr.com/photos/marcpecquet/sets/72157651843338667/
PS: You'll notice some flare on some shots in the second set - I lost the sun cap years ago and they can't be found anymore... Anyway, they were not great. I since got one made of orientable cloth that fits with velcro; as you will see in the first set, the results are great.