I have a 64 oliver 550 with the p/s spill over thru cap. the problem is in the base of the reservior a 90 deg nipple is part of the return line fitting. if this fitting is pointed to the near side wall of reservoir, it will splash out the cap especially if low of oil. solution is to take top half of reservoir off and index return fitting toward far side wall. i also found a 1/2 - 5/8 id fender washer that would snug fit in base of fill neck to serve as a deflector. this cured my spill out problem. sorry so late to reply - just happen to read some old post.