I think the problem lies in the fact she's been sat in the canal at inverness for 2 or 3 years and has hardly moved, the other seams we lost on the way round ratrray head have tightened up a lot with the drenching she got
I think though, that the shrinkage is a good diagnosis, the crack is fairly uniform down the stem, maybe 5mm maximum, there are one or 2 fastenings that might need attention later this year but appear sound for now. I was hoping not to haul her out till after summer is over (which in the UK might be next week!), but wanted to make good as much as I can in the interim...
so putty it is then....thanks for you help again though,