Another vote for benign neglect!
In 23 years of full time cruising, we've never once flushed out our dinghy motors, unless you count the occasional trip up a river into brackish waters.
Result? Johnson 15, vintage 1976 sold in Fiji
in 1990, running well and on original pump
impeller. External bits rusting and falling off, tho'. Replaced with Suzuki 15 which was running fine on its second impeller when it was stolen in Hobart in 2006 (I hope that it fails catastrophically in an awkward place for those bastards)!
Replaced with Yamaha 15 which is also fine,but it is a bit too new to brag about longevity yet.
I do second the advice to wash off the external bits when possible (doesn' take much fresh water), and to keep up the grease regime. These new (2 stroke) motors are bloody marvelous compared to the cranky buggers of yesteryear!
Jim and Ann s/v Insatiable II lying gladstone Qld Oz
PS: Hi to the Klondikes...