I found an Ebay seller that supplies small quantities of AMP Superseal connector sets.  These are waterproof electrical connectors that can potentially replace the not-so-good BMW inline connectors for fuel pump, speedo pickup sensor, etc. or for addition of aftermarket electrical items.  Superseal connectors are fully waterproof so they will not suffer the corrosion and decay that the OEM connectors suffer, especially for those connectors exposed to the elements.

The seller is hiteche.  You'll have to look for "Waterproof Electrical Wire Connector Plug" in the description because the seller does not specify Superseal.  He sells 2-way, 3-way, 4-way, 5-way and 6-way connector sets (male/female housings, contacts and seals) in quantities of 1, 5 and 10 for good prices.  Shipping is free internationally.

I've ordered a few sets for my customization and will update this thread when I've obtained them.

cool