Hi all, I replied to this question once before and got shot down in flames, but I am going to repeat what I said then.
I use meths, but I don't try to clean the brushes of old resin, I just dip them in a small amount of meths wipe with a tissue and then drop into a tall jar with one inch of meths in the bottom and screw on the lid. When wanted next time, I just knock out the bristles on a piece of rough timber and use. It was said last time to use cheap brushes and then through them away. I am still using the same three brushes, I've lost track of time but it must be four years or longer. The same three brushes, one top up of clean meths. Total cost about fifty pence. And no annoying bristles spoiling the finish either.
Strangely, the bristles have all stayed straight, despite standing on their heads.