Lithium and silicone...
Hello,You can get silicone spray (IRC) from electrical supply shops, (don't sub WD40 as it contains acetone which buggers up any anodizing), or you can get LITHIUM - same manufacturer (no UV degradation, food grade, non conductive) grease as a spray from same, apply to your slugs, or one, and run up the slot, if that does not work consider this extreme, I welded loops to a rat tail file and pulled that thru slot with halyard and a downhaul, also lower mast if need be to look for snags or a collapsed slot, usually at spreaders, last would be binding at the masthead rollers, or the angle of your halyard to the mainsails' headboard, keep it as inboard to the slot as possible...SH.