When I purchased the incomplete 750 project from the original owner/builder 7 years ago, he had already installed the fuel tank senders.  As most know, they are '68-77 VW tank senders and the quality is not that great.  If they weren't already installed, I'd have gone a different route but had to live with what I had.  Knowing they might some day have to be replaced, I riveted in the steel retaining ring so I didn't have to deal with it falling in to the tank.  Fortunately, early on I discovered that one of the senders was faulty and had to replace it.  That was easy with the wing off but if having to do that with it on thru that small access opening on the bottom inboard skin would be a royal PIA.  That access cover location should be at least 3 inches forward(see photo #1). 

Well a few weeks back a fuel leak showed up on the right inboard bottom wing skin and it was coming from the fuel sender.  I wasn't about to try and remove it thru that too small access opening so I fabricated access covers on both wings (approx. 4x6 inches) on the top.  I had to drill out some rivets and replaced with 6-32 countersunk(flush) riv-nuts.   The leak was around the pressed in ceramic spade connector fitting.  After removal, I cleaned it up and applied generous amounts of JB Weld to it and the metal base.  Now there is no way that ceramic fitting can move.  To insure that it wasn't leaking, I made a test set up with a spare retaining ring and one gallon can(see photo #2).  Re-installation was relatively easy thru the top. .