I found what I think is a great solution to this problem. I removed the screws holding the top track to the ceiling and tilted the entire door and upper track inward. This allowed me to remove the upper tracks and take the doors out of the boat and take them to a wood working shop in the boatyard in Trinidad. The shop removed the wheels & mechanisms, then routed out a slot nearly the whole length of the bottom of the doors approx 5/16" wide. They then inserted a smooth piece of "King Star Board" marine polymer in the slot and attached it with countersunk screws through the bottom side. I then put a fresh strip of formica plastic laminate in the lower track and reinstalled the doors. Now they open and close with fingertip pressure. After struggling for so long to operate the doors, they now are a pleasure to open and close. Problem solved.
It is important to make sure that the finished height of the doors is correct. I simply told the shop that the polymer" Star Board" could not protrude from the bottom of the doors any farther than then original rollers. The shop determined the width & depth of the slot and the width & depth of the polymer insert. I would estimate that it is approx 5/16" x 5/16" and protrudes slightly from the underside of the door edge. The teak veneer faces of the door are unchanged. The polymer Star Board product is extremely durable and should last as long as the boat. Circe was one of the first Nic 31's . It would be interesting to know if C&N addressed this issue themselves in later models.
If you have this problem, I hope this helps.
Harrison