Here is my story. I have M6 that had that famous flare problem. Simple fix I posted before is here:
http://www.rangefinderforum.com/forums/showthread.php?t=34082&highlight=m6+flare
I managed to jam the shutter a little while back, so off it went to DAG. WHile there I had him do the flare fix, Full CLA, unjam shutter and install black M3 type lever. Turn around was about a month - with shipping both ways.
Was it worth it - well maybe. Full CLA (which he said didn't HAVE to be done, could have done 3/4 CLA for $100 less) made it a bit smoother. Not that much, but some. Flare - somewhat better than that fix I posted above - it is more helpful with VF brightness than flare itself, as tape over that window did make framelines dimmer. If I had to do it over again - I'm not sure if I'd have it done. Keep in mind - My M6 is a user, with dings, and marks. I don't baby it, so I wanted to have it best condition possible, so I had all those things done. I suppose my camera was in a pretty good mechanical condition to begin with, - thats why I don't see much difference from CLA. I love the M3 lever. I could have done lever myself, really, but with CLA there was no extra chage for labor to put it on. I think camera handles better with the M3 lever better. But thats me.
So, what I would recommend - try flare fix I posted, see if you like it. If not - send it out to be done at DAG. I think that's this kind of flare fix is a good thing, but a bit overrated. As I said, I'm not sure I got that much better performance in flare department compared to my own fix. DAG does do a good job and fairly fast. Price is reasonable too, considering it's a Leica service.
Can't help with film scratching issue - but I'm sure he will have some ideas/fixes for you.
Good luck.