these starters have internal seals and are designed for these engines. Most likely you were getting a non-oem starter? Might be the ones you were getting were a cheap aftermarket brand?
I would use an OEM reman or take it to a starter rebuild shop and get it rebuilt there.

Now if the sump housing is building up too much pressure and blowing out the seals in the starter you might have to check the return line and filter and see if there are any restrictions.

If you want any model specific information on anything else we will need to know the FULL model number and serial number.