Water in Lower Unit

Found water in lower unit when winterizing 1999 Evenrude 90 HP 2-stroke. Took to dealer who pressure tested and said it was OK.Thought maybe oil plug not tight enough. They put new grease and plug gaskets in. Used this spring six or eight times and decided to check today. Found full of water again. When I opened top plug I heard it suck a little air so how could it hold a little vacuum but still let water in? One other thing doesn’t quite look right. The bottom plug fits flush or slightly below in the recess but the top plug does not, one side of the screw head is higher than the recess. Anyone have any ideas or similar experience?

Only 2 ways I know of into the unit and thats the lower seal behind the prop or the fill and overflow screws, if the gaskets you put in are doing the job I’d check out the lower seal.

DonG wrote:

Only 2 ways I know of into the unit and thats the lower seal behind the prop or the fill and overflow screws, if the gaskets you put in are doing the job I’d check out the lower seal.

There is also a seal on the input drive shaft directly below the water pump. Also a seal on the shifter rod where it enters the lower unit.

“The bottom plug fits flush or slightly below in the recess but the top plug does not, one side of the screw head is higher than the recess.”
Is the top plug cross-threaded?

2 tests can be done when testing the gear case. Pressure and vacuum. You can have water coming in and it’s still possible to pass the pressure test.
On both the driveshaft and propshaft, there are back to back or double lipped seals. The inner seals hold oil in, the outer holds water out. If it were in my shop, I’d suggest resealing the gearcase