Waterbear:
I have three words for you: Get legal advice.

Why? You have continuing eroding problems that you KNOW will eventually cause some sort of catastrophic failure. He knows it, too, but doesn't want to admit fault or take the expense to fix it.

A lawyer friend of my brother's had a contractor screw up his bathroom, not finish and then had the gall to sue the lawyer! BIG mistake. By the time my brother's friend was done with him, the contractor was paying HIM thousands.

You are long beyond depending on this guy's good will and dealing courteously with him.