I recently noticed the bottom plug/screw on my lower unit is very slowly leaking grease (a couple drops a day maybe). I replaced the old plug with a new one with new seals and it slowed a little more but still leaks. Is there anything else I can do about it or am I just going to be changing my lower unit grease a lot more now? It's a '06 60hp Mercury 4 stroke if that makes a difference. 

Since it is a four-stroke may I suggest you bite the bullet and take it to the dealer?

 

There is a great difference, as you know, between a two-stroke and a four-stroke and although the lower unit performs the same way I would rather you have a professional assist you than giving you personal advice that may sound good but will not work.

Ouch Blue. Thats a tough one. I like Sams suggestion.

If it still leaks with a new plug and gasket I would take it to a dealer and have it checked.  There could be a tiny crack in the threaded area or just a small burr that is preventing a good seal.  I assume no warranty being an '06.