Your lines are probably just fine. Vanagons with older rubber A/C lines that
hold pressure are reported here often. The problem seems to be the shaft
seal, as in all vehicles. Got to use it a few minutes each week in winter
(and summer) to prevent this from shrinking up. Shrinkage of the shaft seal
causes the freon to leakout. A can a year is not excessive at this age, and
if the A/C was never turned on in winter. It is probably best to leave the
connections alone, but if you insist, you can try tightening up on them to
stop any leakage. Be sure to use a back up wrench at each connection.