Dead Puddle & Interior Lights (Superb 2004 Elegance)

2004 Superb (had it since 2006) lost interior lights and mirror puddle lights a few years back (little red ones above dash still work). I investigated water Ingres and removed the drain grommits from the battery well (they were blocked). Passenger side footwell was drenched but comfort unit all clean & dry, no obvious damage. Dried everything out and checked all of the joints down there in the wiring loom. Some were showing signs of corrosion so have cleaned and soldered. Still no interior lights or mirror puddle lights though an intermittent rear window and central locking issue has gone away. Sometime ago somebody suggested it would be a PCB on the mirror wiring (damaged by water Ingres). Skoda told me I would have to buy 2 entire new wing mirrors. Does any of this sound familiar?  All suggestions greatly appreciated, keen to get this car back to its former glory.