Kubota L185 blowing oil reservoir plug....ideas?

[KaLioMele]

There's a little plug on the side of the engine block that the tractor keeps blowing. We figure the first time it was just due to age, but when we tried to replace it, we got about 4 hours out of it, then it blew out again. Spews oil everywhere...

Perhaps is it supposed to be reinstalled from INSIDE?? How would one do that? What are we doing wrong? Got the correct part number, worked for awhile.

Thanks

Hil