Making flyback transformers?

As some of us know all too well, flyback transofrmers fail, and are often next-to-impossible to get. So I have been wondering if it's possible to make a replacement... There would appear to be 2 parts to this. 1) Desigining the replacement. I think we can assume a schematic of hte horizontal output stage it's going to be used in. But how do you calcualtor the number of turns on each winding? Since the origianl is likely ot be potted in epoxy (for HV insulation reasons), counting the turns there is impossible. Are there any good references (books, web pages, etc) on the desing of such transoformes and/or the design of horizotnal output stages? I would have thought something must exist, but I've never seen it. 2) Making the replacement. It owuld ahve to be vacuum pmpregnated, I think. But I believe some model engineers who make internal combustion engines make the own ignition coils (and vacuum-impregnate them?). Again, any good references on doing this? -tony