Mineral Spirits Vs Acetone

For the oil base I suspend the brushes in MS for the short term, overnight or a couple days max. Any longer, if I plan on keeping the brush, using MS, I'll "paint the brush out" on some cardboard laying around. Takes a while but I've had favorite brushes last for years. BTW, If there are small dry paint spots I've used a file cleaning brush on the bristles with some limited success.