That is the only similarity between the cameras. The mirror (semi transparent), mirror box, mirror lift, shutter, shutter release, lens mount, top and bottom plates, metering system, auto bracketing, electronics, preview, timer, etc. were all Leica and/or to Leica specs. Also, the Leica R4 to R7 were beefed up from the Minolta based chassis.
Originally Posted by Uncle Bill
The original R4 was known to have problems with their electronics. This is in part why the R4S and later R4SP were introduced. The R5 did offer the first TTL for flash of the Leica R series cameras. The later R Winders were an improvement over the original R4 winders.