Most of the bottom cover was covered in a thin film of water with a patch about the size of a matchbox (50mm x 40mm) that had green tinged foam/slime around it - that's where the BMS's daughter board was sitting in the pool of water!
BMS daugher board circled in red. (Daughter board appears to be so they can use the same BMS for 12 or 16 cells systems. They add four more cell handlers on the little board.)
Unfortunately my sense of WRONGness was so great I instantly wiped it all up - then remembered that I should have taken a picture - oh well.
I removed the BMS board and cleaned it with genclean (PCB cleaning stuff) then resoldered any suspect looking pins (a couple of Molex pins looked like they had corroded slightly), then gave the board a coat of clear laquer.
OK - so where did the water come from.
Some while back I crowed about how the Vogue was fine charging in the rain because the charger inlet (located IMMEDIATELY above this water soaked pack) had a "moat" that went to a drain hose. Well the 48 year old drain hose had cracked even more than when I re-installed it and was leaking every time I charged in the rain. Also, any water that got under the unsealed cover while driving went down the drain hole/hose.
The charger inlet, "moat" and drain hole in question.
I cut the bad end off the hose and ran the hose in a straighter line (no fuel tank to go around).
View inside the boot.
This old picture shows where Pack #5 is mounted with respect to the charger inlet. It's the one sitting alone on the left under the contactor/fuse box.
I haven't tested the BMS board yet to see if it still works - fingers crossed.
I'll try to get the pack back together tonight - it's still in the state of the first picture in this post.
When I re-install the pack (assuming the BMS is OK) I will put a temporary cover over the pack and check it regularly for a while.
I am still amazed that the water had got into the pack enclosure so easily. The three packs under the front of the car (engine bay) have been sealed with waterproof gaffa tape but now I wonder about them as well. At least their orientation would not have the BMS board at the bottom of the pack like this one.
...and yes, I am very embarrassed.