here are some pics of my lower from 1 of my 300x's. any input would be appreciated. i've heard from a few it is common but mercury's racing division hast acknowledge'd that yet. going to have it welded again and we'll see what happens.

few more

and more

Never saw that before.
The second crack may very well have been a weak point from the heat effected area of the first weld. As for the first crack that was welded, dont know?
How many others have you heard about cracking there?

Now I see where you are talking about welding a plate on the inside (post#3), I would do it. No reason you couldnt. That will strengthen it vertically which is how it is cracking now.
I would have someone look at the shafts, mine were worse but it might be covered under the corrosion warranty.

i just emailed Chris at Mercury's Racing Division all the above photos and we'll see what he says. He supposedly has an excellent repor with Rolf at ProRoc so time will tell. I've spokin with a few people and it isnt an everyday occurence but it does happen. Rolf said its fairly common and so did the welder i spoke with.

Bernie,
Post it on that skeeter killer site, Im interested to see what they have to say over there.

its mercury, junk...... thats the problem...

I have had some lower problems on my 300pm in the last 4 years but not what you have there. Must be a casting problem. I know Philip on the board has had some cracking problems with his lowers. He runs a 32' skater with twins. I figured the heaver boat was over stressing the cases but now I don't know. Think about this... If the heat treated factory case cracked what makes you think a welded case will hold up? Best repair, buy a new housing ans install your internals. As Tantrum says welding weakens the aluminum in the heat affected area..

This is a post for screamandfly.com , lots of wakkers there.