Just a thought ,as it’s been mentioned before, link between head gasket and shells. My gasket went between 1and 2, The rod bearings number 1 least worn And ok ,,most worn bearings was number 6 rod bearing , that’s the piston on the opposing stroke , so possibly to do with uneven loading on outer ends of crank ,, Olso noted that it’s a more even wear rate in other inner cylinder rod bearings,,, food for thought chaps ..
