I have an '88 Sentra with a cracked head, casting #52A. I've had a horrible time trying to find a replacement. I've read through most of the threads on this site, and there seem to be more than one casting number that may work on my car. Does anyone know if the 52A can be found anywhere, and if a different casting number work just the same? This is only a commuting car, and until I had my problems, I was clocking 34 gpm....I'd really rather fix it than retire my faithful friend. Thanks.