Diff locks

[DGraber460 at aol.com]

Some time back I posted asking if anyone had made manual controls for the  
early diff locks replacing the vacuum operators.
Several posts related that it had been done, and most referenced electric  
solenoids.
Well - I tried manual cable controls (like the throttle control on a  lawn 
mower) only to find that it could activate/lock the rear diff, but did not  have 
enough strength to disengage.
Trying the vacuum system again - it would also engage but not  disengage. 
Checking all the lines again I think I have a leak just above where  the tubing 
enters the uni-body. At that point they are not accessible from the  interior, 
or below.
Does one have to remove the fuel tank to check and repair this portion of  
the vacuum lines?
TIA  
 
Dennis
Denver