61 G80CS Inlet Rocker Failures

[ranger]

Had a number of inlet rocker failures on my 61 G80CS. 2 valve end rockers snapped some time ago which I put down to possibly the head steady tightening sequence distorting the head in area of inlet valve. Fitted new rocker arm and I left head steady rear bolt loose, problem seemed solved. Early this year had inlet rocker shaft snap at valve end spline area. Sent it for analysis and failure was fatigue emanating from original old mechanical damage to spline area. NOS shaft fitted with original rockers. Whilst dismantled, had new close tolerance Nemesis guide liners, new seats/guides and was told by machine shop that inlet valve oil supply not now required so tightened supply needle fully home. After re-assembly, bike running better than ever but after 100miles, inlet rocker (push rod one) has snapped!
I’m sure my valve clearances are correct, valve lift is correct, cam is correct (C1), push rods are correct. Has anybody, please, any ideas as I’m pulling my hair out. However, am keeping fit as the last push home, 4.8 miles, was done in 1 hour! OK there were some downhill bits.
Many thanks in anticipation