I'm sorry to hear about that happening to you, it was a PITA! I tried having it welded, but the boss just melted. From what I have read, cast aluminum is very difficult to weld on, especially when it's contaminated with motor oil. I ended up getting SOA to chip in on replacing the entire cylinder head. They provided the parts, and I paid for labor. It's ended up 50/50. Looking back, the only "quick fix" i would have tried prior to a head replacement would be some type of liquid weld. You can try one of the "JB Weld" products or RTV liquid gasket. I would probably try the RTV and put a coat on the threads of the new oil sensor before threading it in, then maybe JB weld on the outside of the cracked boss. Good luck!