Hi mate thanks for the reply, do you mean getting the crank split to do the centre seal or the outer two? Is it a difficult job as I have rebuilt 4 stroke heads before but never split cases to do bottom end work?

I did do a bit of reading up and mc16 seals are NLA but later ones will fit but will be recessed rather than sit flush, looks like the engine build might be delayed a little longer as I have the seed of doubt in my head again lol, I'm guessing failed crank seals let air into the cases and cause it to run lean and sieze up?