'98 GTX RFI overheating and crack in tuned pipe head.

[Nu2PWC]

I was out with my boss and his family this weekend. I just finished fixing his GTX MPEM's (Thanks Mike). I was on my HX and after about 5-10 min of riding his GTX quit. We towed it back to shore to have a look. Diagnostic mode showed Hi-Temp. The welded in plug closest to the band clamp on the underside is cracked and leaks water. Let it cool down and it runs til it overheats and shuts down again. What would cause it to overheat? Is it the cracked plug? If so what caused that? (My boss fried the MPEM's beginning of last season so i don't know if they were fully winterized last winter) Any or all help would be greatly appreciated. Thanks