Noooooo! there could be a number of reasons its seized.
first, can you rotate it with no power?
if not, take the winch off the top, there are 4 screws on the bottom, undo them and gently pry the top off. be careful at this stage. this is where the gears are. carefully check all the gears, to ensure they are meshing. they should, looking from the side, be horizontal. if one is on the slant, this is where the problem lies.
now, if there is still no obvious problem, checking for swarf, dust, dirt etc. then if you confident, disassemble the gears, making sure you remember the order they come apart in. check each gear tooth for damage of if one or several is missing.
once the gears are disassembled, plug the servo back in and see if the servo motor works. if it doesn't, then unless you nan get a similar motor, the servo could be a write off. if it does work, and you have not encountered any damage, reassemble the servo, using a light to medium grease, NO OIL, CERTAINLY NOT WD40. I use lithium grease from B and Q. check at all stages that everything is level and non binding.
hopefully, although not conclusive, this should hive you a little insight into repairing a servo. check youtube, plenty of videos of how to strip and replace gears in servos.
