How does one know if they have the older style lower unit or the new style lower unit. I bought mine new between 2005-2007. Can't remember specifically until I get home, but thought maybe someone could give me some early insight.

If I need to change the tower housing sleeves is it best to update the lower unit then? What's the problem with the old unit?

umm what brand?

Assuming you are talking about a pd...

The older one's were more likely to leak. You don't have to change it unless your having a problem. If your's has never been replaced, you have the old style, but if you aren't having any issues, there is no reason to replace it.

The newer ones are filled with grease on the bottom and top. Basically making it where water can't get in the gear housing from either direction. The one they released a couple years prior to that had grease in the top. The one you are running now is just full of fluid, no grease.

The newest LU is from around august 2010 as far as I know, mite b a newer one than that. If your prop shaft seals aren't giving u continuous trouble I wouldn't bother with it.

Your not going to gain anything by swaping it out aside from fixing a leaking seal.

The first change came in 2008 and is when they started using 6 bolts to mount it instead of the original 4 and changed the way to keep water out. Also was when they started putting a larger gear box on it for the opportunity to put different gears in for different applications in the future.

Not sure what's different now.