1998 500 MXZ had oil leak out of tank last winter. I replaced rubber grommet in bottom of tank. This summer, same thing, all the oil leaked out of tank and it appears to be coming from same place, and it appears grommet is bad again??? Any suggestions as to other causes or long term fixes?

Clean the reservoir well with hot soapy water. Apply baby powder to lower part of injector oil reservoir. Now wait a few hours an verify where the oil is seeping. The powder will indicate traces of the smallest leak. Leaks aren't always the grommet, that happens to be the low point of the reservoir.