Just rebuild it, the LPR on Wraths is just about bulletproof, all it should take is a couple of correctly sized o-rings, shop just probably wants you to buy a new marker from them. If you need help just take it apart and post pics of the internals.
This is what it should look like:
If you turn the LPR adjustment all the way out and still hear a leak from the front or side bleed, it's the small o'ring between the shaft and the body of the LPR (2nd from the right) if you don't hear any leak it's the piston o'rings (on the brass piston).
If it's the shaft o'ring let it soak in pb oil for a few minutes and re-install, if that doesn't work then change it.
If it's the piston o'rings then, if the o'rings are dry and not knicked or chewed up, try lubing with oil, if that doesn't work try dow33 if that doesn't work try dow55 if that doesn't work then it's time to change them.
If neither are to blame then the leak should come from the base of the LPR and you need to inspect/lube/change that o'ring.