Hi Chris,
1) yes,TR1 engine uses a sprag clutch
2) clutch is behind lhs engine cover, no need to disassemble the complete engine or starter
3)difficult to fix - no, if it is really the clutch. Please see the microfiche in the "technical information" on this site, on page C7 and C8 you will find some illustrations for starter and clutch. Engine cover needs to be removed, and starter drive gears plus solenoid and appropriate linkage needs to be removed. Clutch can be exchanged, if you have a new or better part - but it can also be welded together, that there cant be any movement in the clutch furthermore. I have done this several years ago already, without any negative effect to the starter.
However, it must not be the starter clutch. The clutch was the first solution I tried to resolve the same problem, and it did not help at all. Reason for slippage in the starter drive was a slipping outer gear ring of planetary transmission inside the starter assembly. Refer to microfiche C7, the part of starter housing located between partnumbers #3 and #9 includes a planetary transimission, where the outer gear ring should be fixed to the housing. This one was loose in my starter and could not carry required forces to turn the engine. On this website you will find many solutions for this issue, unfortunately most in German. Some guys are using additional washers, my solution was 2 component glue, to fix the ring in the housing again, and it works since many years now.
Complete new starter transmission is sometimes offered in the Internet.

Hope this helps you out.

Jürgen

Thanks Jürgen,
I owe you a beer! The outer ring inside the starter is VERY loose.
Easy to fix when you know the problem
Ride safe,
Chris