Hi All- I am looking at a M20J to purchase. Both wing fuel sumps have blue stain around them, and I am assuming that they can be repaired with new o-rings or seals. But there are also a few ( 5 or 6) rivets under the left wing that are outlined in blue (see photo.) When is it time to address such an issue? What is your experience in the progression of fuel leaks once it is first noticed? Thanks very much for your input.