When installing new transoms should there be any sealer used like 4200?Merc. book just shows to use a little lube,like 101 on rubber gasket.Is this all it needs?Old transoms had some silicon at the bottom around the two lower bolts and it looked like the gasket was glued in place,but it was also 15 years old.Any suggestions?

Thanks Nordic95

I use Sikaflex for sealing transom. Looks more like urethane than silicone. once installed and dry... tough job to take it off!

I like to use 3m 4200, merc says you dont have to use anything !!!!

mine was a 96 and could see where bolts had been over tightend and inner piece of the sandwich had cracked and transom had some waves in it.... i used 4200 both under the gasket and on the transom and it took care of any worries. i think if i did another one i would use the urethane sealant that is used to install windshields in cars... tough like crazy but remains just a bit flexable and bonds line its born there.

I usually use regular silicone. Merc says install dry, but old transoms usually have irregularities and might not seal well. 4200 can be a bit difficult to remove if you need to take it off again, and 5200 will take the gelcoat off with it.
Gary

What timing. I have mine off and it was sealed with a little silicone. I like silicone on some applications but am looking for better alternatives. 3M 4200 seems like a good choice but I am a little worried about removal the next time. I was thinking about using a urethane sealer made for use in wet conditions. I too am curious what most others use. Dry seems like asking for trouble.

Jeef which Sikaflex do you use? Looks like a good choice also.
http://www.sikaindustry.com/ind/ipd-ma-products

I replaced my transom assembly 2 years ago and used only the rubber gasket from Merc., no sealer at all. I have seen no leaks at all and leave the boat in the water 1-2 weeks at a time during the summer. Boat is a 1988 wellcraft nova spyder, single engine.

I have seen silicone used on many. I use a little 5200
Silicone is really not for use under the water line, and silicone promotes corossion. BBB