Except for that there is a wast difference between RD-1's 1,5 and M8's 1,33 crop factor, the M8 is a far more reliable. - Except for this Red Line Issue. 'All' the 2.hand M8s' on the Norwegian 2.hand market have been to Solms for repair (pixel remapping device installed). Then they will work fine for many years. The rest of the camera has proven to be very reliable. The 2.hand M8s out there are better than they were new!
I have tried to buy a decent (mind you) RD-1 for years. - I started this process even before I bought my M8 back in 2006. Now I have given up, though. I have looked seriously at 5 units 2.hand RD-1 for sale here in Norway and Sweden over the years. All of them had some kind of service issue or malfunction. From framelines all bungled to lcd screens not wroking. Having in mind that Epson don't market the RD-1 here in Norway and have no service system organised. You are on your own. Several of the Epson RD-1 sellers was so pissed off by Epson that they had promised themselves that they should 'never buy a Epson product again'.
The Epson RD-1 is one of the most charming cameras launched in the last 10 years. A major break through as a product idea. But Epson did nothing - absolutely nothing, to follow up on this success. Nor to follow up their original RD-1 customers. What a shame! Nor were the product quality up to that of Leica.
Leica has a good service system (but slow, some say), and Leica is known for sticking to their customers, and be reasonable regarding serivice cost. Several 2.hand buyers of M8 have had their cameras Red Line Fixed for free.
2.hand Rd-1s are dead fishes in the water, which the supplier has given up on. While 2. hand M8s are good cameras with a long life in front of them, with full backup from the producer.
That choice is an easy one.