Another thing you might want to look into is the position of the plate holding the worm block. On my mount it is threaded into the RA body by 3 screws. There is a bit of play with the centering which affects the distance and orientation of the OPW in reference to the spur gear edge, hence the worm possible meshing range. If the gearbox side of the worm is a little tight you might want to move that plate slightly off center towards the OPW. That will give you a bit more gap. Not too much forward or the maximum meshing will still leave you with some backlash.
