Hi Frank,
If you had a master cylinder snag you wouldn't have been able to bleed the other brakes, so I don't think that is your problem. Unless you are allowing the master cylinder to empty whilst bleeding you won't introduce any air there. There are kits to allow reverse bleeding from the wheel back, but I don't know how much they cost. You should only have to do about 10 pumps maximum per wheel and thats if you've had the system apart!
I will go off and have a think.
Cheers now
Ken Chapman, April 2007