Rockshox Reverb - sticking down

my 125mm drop reverb has just developed the problem of sticking in the fully down position. it will come back up if i give it a little pull.

also if i dont put it fully down but leave it say 2cm up from down, it will come abck up without sticking. i havent changed anything that may have caused this change (etc over tightening the seatclamp).

has anyone else experienced similar problems. can it be fixed by a bleed? i just checked the air presseure and its still good at 250 psi.

Thanks for any advice you can give.