what would cause the factory merc high gloss paint to dull ? boat is left in fresh water for 2-3 weeks

If it is white looking on just some of the drive, it might be lime that cooks on as the drive gets hot. Try Tub and Shower lime remover at Krogers, etc. Put it on and rinse immediately. If this is the issue, it will look like new. This works good on the exhaust tips as well.

Sitting in the water for long periods of time will cause the paint to fade/get dull. You could rub it out with some light compound and wax it.

Having a drive shower reallys helps avoid the condition. Easy fix is spray it down with armour all tire shine. Looks like new in seconds. Just have to reapply every time you use it.

lime away

After the Lime-Away I discovered that using Meguiars #45 polish really brings back the deep, glossy black. Makes them look like new. Follow that up with a good wax.

I also leave my boat in freshwater for the summer. I use 3M Finesse It 2 to bring back the gloss polish. Works wonders to a dull faded drive.

If it is the "lime issue", white vinegar works extremely well,
even on exhaust tips.

Ken