That's exactly what I was thinking when you posted - but didn't want to!
First set of readings - battery not fully topped up, but that didn't matter.
Battery voltage= 4.06v
Voltage at 510 =3.62v That's too big a loss?
Switch is bonded into the resin on the mod and appears to be a sealed unit - none the less, a squirt with contact cleaner around the fire button and a bit of working there was some slightly dark residue to be mopped up.
The wiring connections to the 510 were gunked up with old juice - more cleaner and a cotton bud had it looking better but not perfect. When I've a little more time I'll do a better in depth clean-up.
Next set of readings are much better, battery still at 4,06v with 4.05v at 510....much, much better!
Fitted an attie with original Kanthal builds and it's certainly improved. Not how I'd just like it, but I'll get a SS build with a lower ohm value and I feel sure I'll be on my way to squonking nirvana!
Again, thank you for your contributions