The cast aluminum mounts are very reliable. Whats not is the rubber disc that separates the halves. It tends to collapse on the engine side, which puts a bending moment into the 3/8-16 bolts into the block. The bolts break, so instead of replacing the rubber, guys put in grade 8 bolts, or drill them out oversize to 1/2". The bendng then transfers to the cast mount... Do NOT replace the rubber discs with polyurethane. It gets very hot under there near the headers, and the poly will melt. Second, a broken mount is often the first sign of a hard collision sometime in the car's past...
