Seems a simple thing, but I have started having problems cleaning paint brushes after using oil/solvent based paint. In the past I have always used white spirit, followed by warm running water and washing up liquid. But lately the bristles never seem to come clean. They always feel a bit "greasy" and when dry are quite stiff, so that I have to bend them back and forth to break them apart. But they never seem to be as soft and flexible as when new. Have they changed white spirit in some way so that it isn't so effective? Should I use a specific paint brush cleaner? I always thought this was just another way of getting more money out of the unwary. I would be really grateful for any advice.