[SkunkBoat]

OK, I looked at it today and got the scoop from the dealer. Here are some pix to show the problem area.
There is a plug in the port side of the "engine holder". This part is on DF90 thru DF140. The plug is ferrous metal in an aluminum housing that has hot exhaust behind it. It was intended as a potential place for service to install an O2 sensor which they ended up never using. The corrosion is from the inside out. Its not salt corrosion because there's no water there. Its bimetalic corrosion and clearly a defect in material or design. My guess is cheap chinese stainless steel plugs and some get lucky, some don't. Hence, Suzuki has stopped tapping/plugging the hole in newer models. I didn't ask what year. Mines's a 2004.
The dealer said he has seen it in 3 older engines. One was in a twin configuration with one motor badly corroded so they took the other apart and it was fine.
Estimated cost to repair $1800 ($1018 for parts). Hopefully he doesn't find corrosion in the head or oil pan.

By the way, I got the picture off The Hull Truth site where someone else had exact same problem but looks like a Johnson 'cause its white.