I bought a tin of that "milky" thinner at a hardware store, it doesn't belong ANYWHERE! I store my household rattle can nozzles in a glass jar filled with thinner, for many years this has worked well for keeping them useable like brand new. When I needed to get more thinner I bought that milky stuff unknowingly, poored out the last little bit of the old and replaced with the "new". Next time I had a need for a can of paint, the nozzle would not fit in the top of the can, the plastic had swollen so severely. About 12-15 nozzles were in the bottle, so I marched everything down to the store where the thinner was purchased and got hold of the manager. My complaint was backed up by the condition of the nozzles, the plastic was actually changing shape from being so distorted and swollen. He replaced all of the cans I brought in to show him, he had not seen the problem but agreed the thinner had to be the problem.
Don is quite correct, make sure of the contents before purchase. If you find it's the milky stuff when you get home and open it, immediately return it. Even better, ask an employee to open it at the store and check that way.
Patrick Stack in Oregon