I have 2002 Mercruiser 5.0 MPI sterndrives. Winterinzed it today and had an issue with 1 thermostat drain plug. It seems the thermostat drain plugs are different size than the 3 block drain plugs. Does anyone have a part number for these? I purchased a replacement block drain plug and it didn't fit (18-4226). One of my tstat drain plugs works great on both engines, and the previous owner "made" the wrong one fit on the other engine.