Looks like my problem is solved. I rebuilt the front calipers (again) with new seals and bushes, the pistons cleaned up as new. They were awfully gummed up inside though, surprising they applied or released at all. It also seems that one of the jobs I thought was done years ago was in fact not, must have just slipped past and forgot to tell me. The other problem was that even though the casting numbers on the calipers matches those used on 77-78 models, the bleeder screws and banjo bolts were metric. So some were either introduced before 79 or the same casting numbers were used over the different versions, makes ordering parts fun, wait weeks only to find they are wrong and you are stuck with them!
