The most likely place for it to come from is indeed the shaft itself, assuming it's at the shaft/handle. The leak can often be resolved by removing the shaft form the topside underneath the black plastic nut (5/6 sided?). There are 3 (I think) o-rings on the shaft and they need lube. On a regular basis just a shot of silicone down the shaft will keep things OK. Now when you disassemble you might put a bit of dielectric grease or similar to get a more of a seal and you can use the silicone every 6 months or so after that. Worst case, just replace the o-rings and you should be good to go.