I sent my older dacron sails to SailCare last year, and they came back looking and performing great. There web site is Sail Care for sail cleaning, sail repair, new sails, roller furlings and sailing equipment
and they will answer questions for you. They typically do more than a "cleaning" of the sails, but the reconditioning was what I was after anyway. This is more expensive than just having them cleaned at the local lost, but when I did this before with our local loft, I was not happy with the repair or quality of the cleaning. They also do minor adjustments, for a fee, or course. I sent my racing composite sails back to the local loft when I need them cleaned or repaired.