Lloyd- thanks
I trawled around rangefinderforum, l-camera forum, and google pointed me towards nemeng.
Mine was the simplest kind of adjustment.
I knew the close focus was off, but then noticed even at infinity my RF patch was not 100% lined up.
Thus the whole range was off.
Properly set infinity, and the whole range is on again.
I read far too many posts, but these were the most helpful-
nemeng - followed the few short paragraphs at the top under "Horizontal RF Adjustment".
l-camera forum - This is a good step-by-step, though for M8 I used a 2mm allen/hex. Note I only adjusted (B), as my infinity was off. I did not touch (A).