Goretex comes in two common froms, two and three layer. The difference being the presence of the inner layer - usually a thin blue woven layer that serves to protect the membrane. Clothing designed to be worn with other parts of a structured system seems to sometimes omit this layer. The membrane itself is white. And it isn’t very strong. If the blue layer is breached you know you have a problem. Aquaseal is a good (acutually I find about the only really effective) product to fix it.
My experience with sailing gear is restricted to my dry-suit. It is a three layer fabric and is fully waterproof. But it does wear. I find it wears at friction points - and areas of very high flex. And a dry suit is no fun if it leaks. I sail an off the beach cat, and get abrasion off the trampoline mostly. However it is maintenance of the zip that is the real key to staying dry.
I have had other waterproofs, and beathable waterproofs that have totally failed when their unprotected membrane has simply delaminated from the main fabric. On the whole they are very poor value. I think the point about oilskins is well made. The nature of the proofing is such that yolu raeally have a saturated fabric, and the proofing migrates constantly. Only whne the fabric is actually holed will you lose the water resistance.