as you described "sticky second curtain", can you post sample scans of your film rolls/shots. my CLE developed something like that description. but your further explanation isn't similar to my experience though. what happened in mine is that some frames had half frame with the image and half would be black. eventually this aggravated to some frames being full black, then further... all frames unfortunately.
direct lubrication and cleaning by some local stores didn't help. i then sought help from a US based repair shop which then returned it with a note that they cannot repair it. they had recommended a change of the motherboard.
what's inconsistent with a replacement is that all of the metering was working fine wc means the electronics were all working properly. like your description, all mechanical. alas, my cle was "dead" apparently.
after about 5 months, i finally found a local technician who said he found a small screw wc he tightened so that both curtains synced properly. he then put a small amount of cement glue/cyano acrylate to make it permanent and hold firm.
i'm hoping that this is similar to your unit's problems and can be rectified.
btw, i only use eveready alkalines on mine as silver oxides are not locally available. not much problem there, metering is spot on. just need to replace batteries more often probably than if silver oxides were used.
hope this helps.
i'm so happy my cle got "revived"!
Leica MP 0.85 | Leica M8.2 | Minolta CLE
Voigtlander 15mm/f4.5 Super Wide-Heliar | Voigtlander 35mm/f1.4 Nokton MC | Leitz Summicron-C 40mm/f2 | Leitz Elmar-C 90mm/f4
Nikkor-P 45mm/f2.8 | Nikkor 50mm/f1.2 | Nikkor 50mm/f1.4 |Micro Nikkor 55mm/f2.8 | Nikkor 105mm/f2.5 | Micro Nikkor 500mm/f8
Nikkor 17-35mm/f2.8 AF-S | Nikkor 80-400mm/f4.5-5.6 VR