Scott,
Some guys have had that type of problem and we've been using the 25 x 25 mm fan most of the time because it seems to hold up to shock better than the stock one.
Cookie,
Yes, most of us ran lightweight motors. Craig Drescher, Josh Numan, myself all ran lightweight 3.5s in our touring cars and Tosolini ran a lightweight 4.5 in his 1/12 car.