I agree with Psneld, if there are no active elements in the lower mast, just paint it and forget it. If, however, it is active, avoiding metallic paints seems to be the the common advice from electronics pros.
If the antenna is really old, while you are at it, you might also inspect the coaxial cable for signs of deterioration and especially check the connectors for corrosion etc. Most antenna performance issues are related to the connectors and cable, not the actual antenna unless it is physically damaged.
When you are done, if you haven't already, try out the Sea Tow automated radio check system. Just make a call on VHF 26 or 27, and a couple seconds later, it will be rebroadcast back to you, so you get to hear exactly how well you are transmitting. You can check here for the station location nearest you:
https://www.seatow.com/tools-and-edu...ed-radio-check
Happy painting