
Does not sound too serious then, in fact, he may just be a bit slack and there is nothing you can do about it, think I know the breed but may be wrong - some breeds do tend to loose pasterns with no really problem (not even in the ring). Not sure there is a lot that can be done exercise wise as it is the tendons not the muscles that seem to be too lax and if anything exercise will make worse not improve.
If your vet is good on conformation I would ask their opinion but if not you may do better to ask someone you trust in the breed or better still two or three and get yourself a selection of opinions.
Know what you mean about coming down hard on your own, have stopped showing sometimes because I think there is a glaring fault and then I watch my breed being judged and see others far worse and put mine back in the ring, get placed badly and ask the judge why he is not liked and was told he has a small white mark on his chest, he has, but that had not bothered me at all and I do sometimes wonder if you enter enough shows you can make up all but the 3 legged.