No problem with ours either. However, if it starts getting fairly windy (say 25kts) I put a little more tension in the line using the winch. Hand tension sometimes isn't enough. You can't put too much extra tension on so if it looks likely that conditions will worsen (30-40kts) I do go forward and pull the lever to lock before it gets too wild.
I'm in San Francisco bay, so most of the time it's blowing between 15 and 30 kts. I spoke to a rigger who says that he has replaced several of the furling line drivers. I made an inquiry to Selden, but getting a response from them is like pulling teeth.
Assume this is a selden continuous line system? Have a look at ybw forums as a mate has this and has some tips. The main tweak he has made is to make it so he can control the ratchet lever remotely. He did this by fitting bungee to lock it and then a small lanyard led through a cam cleat to release when furling.
Selden's reponse to my inquiry regarding slipping/unfurling were as follows:
Be sure the ratchet is engaged on the line driver when furling so that you aren’t fighting the sail.
We recommend 10mm 16 plait line. Also check your furling line driver because sometimes after many years, those will wear down to where there is not much grip. If that’s the case, you can send the entire unit in for a replacement of that part.
I responded that they first recommended New England Sta-Set Double Braid Rope 3/8" 10mm (in the manual as well, 10mm double braid). Selden response: . 16 plait is more “bumpy” of a line, so there is more friction. Al-la knobby jeep tires versus racecar tires with no texture. Use a 16 plait and see if that fixes it.