IMO, WD-40 is not a lubricant and should never be used. If you want to use the exsiting jib blocks take the time to disassemble the entire setup.

1. Use soap and water clean them, then rinse everything off.
2. Let all the parts sit in a bowl of CLR for a few hours.
3. Rinse again and lubricate with dry Teflon spray and let them sit overnight
4. Put everything back together and lubricate again with either dry Teflon or Silicon spray.

I do this once a year on all my blocks and mine are only a year or two old Harken brand. When stuff works like butter, sailing enjoyment is 10-fold.