I just serviced the two Furlex units on my Stevens 47. Mine are earlier models than your 400s, but the basic architecture is the same. There are bearings in the bottom unit, which carries the whole weight of the foils and which must turn freely for the furler
to work properly. These bearings, as well as those of the upper swivel, must be cleaned and greased periodically (at least once a year).
So, did you grease the lower bearings as well as the halyard swivel bearings?
Greasing the upper swivel is easy. Spray some brake clean in the bearings while spinning the swivel and then grease them with furlex grease.
The lower unit is much more difficult. There are two bearings. See the manual on the Selden website for instructions on greasing them. If they're anything like the bearings on my units, it'll be a bit tough. The lower one is pretty easy to get to: it's on the bottom, just above the stayloc terminal. Clean the bearing with brake clean and do your best to force grease into the bearing. For the upper bearing, pump grease into the hole "A" and hope for the best.
If greasing the lower unit bearings doesn't solve your problem, the entire lower unit can be disassembled and the bearings replaced, but the parts
are expensive and it's a lot of work. You'll have to pull the headstay out of the foil to do it, and you'll have to replace the wire when you do so. If you have to go to all that work and expense, IMHO, you'd be better off buying
a Harken furler
. It's a much better design: more reliable and NO grease!