2000 V70 SE, Denso, AW-5, 278K miles

Been chasing this gremlin for a long time: Misfire on cylinder #3. It occurs randomly, CEL lights up, and after fixing you can count on it occurring again, with no predictable interval between episodes. It can be after 10 miles, 100 miles, 1,000 miles, but the misfire and CEL will always re-appear and it's always cyl 3.

All my troubleshooting and fixes have worked, but only temporarily. Have swapped coils, installed a new #3 coil, changed plugs, repinned a new #3 coil receptacle housing (twice), spliced (crimp + solder) four new wires from the #3 coil as far upstream into the harness as I can get, and checked/cleaned all grounds. The car will run great after the troubleshooting and fix, until the misfire / CEL occurs again. Always #3. The local Indy shops are stumped - no help from them.

Because the engine runs so well when all cylinders are firing, I have ruled out a cylinder compression issue but had it tested anyway at the Indy shop. All five cylinders test at over 160.

Some will suggest that an entire set of new coils might solve the problem (why I'm not sure, if there's only one problem cylinder). Some will suggest the ECM has a problem with triggering #3 coil, or high resistance in a coil wire somewhere along the routing from ECM to coil.

Regarding the ECM, can it be unplugged, terminals cleaned and then replugged? Ocean salt air corrosion takes a toll on electrical connectors here, and so the V70 would not be immune from corroded connectors.

Q: Can Xemodex or other vendors test check the ECM, before saying it needs to be rebuilt?

Any ideas appreciated,
Robert