Outdrive to Gimble housing

[Earp]

My project boat is a 20 foot cuddy with a 4.3l cobra.
Recently had it in the water for an hour or so and noticed a trickle of water coming from inside the transom bracket, it is too hard to see exactly where.
The transom is new as are the bellows and gimbal bearing.
For some reason I was under the impression not to use any gasket sealer on the large gasket between the outdrive and gimble housing, howeverI was just searching through posts trying to get some ideas where my leak is coming from and found an article saying to use OMC gasket sealer:facepalm:
I thought the gasket felt like a cheap scrap of paper and didnt think it would do too much to keep water out.
Is this the obvious first place to start with the leak?

 

[Earp]

What about the Y-pipe where it bolts through the transom? I was thinking this could be the source of the leak, however i ran it for hours with the lower half of the outdrive in a water tank but it did not leak. What are the odds of the trim sending unit wires leaking? I tried filling the bilge with water up to the starter and there was no leak on the outside. Any other tricks to find a hard to see leak? I am planning on backing the boat in the lake in stages to see if I can narrow down the area of the leak, just need a calm day.... thanks for any help!

Earp

 

[Sparkinator]

I tried filling the bilge with water up to the starter and there was no leak on the outside. Earp

I wouldn't try that again. Unless the keyhole and studs for the drive are completely sealed, water can get into the transom core whenever the water level in the bilge is that high.

I've got a Cobra SX (95) and just recently rebuilt the transom. When I mounted the transom shield to the transom, my manual called for 3m scotchgrip rubber adhesive 1300 applied between the new gasket and the transom shield. It's also used on the ends of the gasket to seal it together. The ends of the gasket should also be at the top of the transom shield. (So it will be less likey to be under water). From what I read, the 1300 isn't applied between the gasket and the hull of the boat.

Gasket sealing compound is used on the transom shield studs and on the gasket for the exhaust Y pipe.

Not sure if this is applicable with your year drive though.

EDIT: 1300 is called for on the exhaust Y pipe gasket. Gasket sealing compound is called for on all the studs and for the shift cable sleeve. (not sure if you have one of those).

 

[LAC_STS]

Did you check your shift cable tube? Dunno if you have one on your engine but my Cobra has a 1 1/4" tube that the transom shift cable comes out of. It has a fitting on the other end and it screws into the inside part of the transom assembly. If you have an OEM manual they have a good picture of it in the section about routing the transom shift cable.