epoxy resin in the tube is really good on lead you can get this from most poundland stores it comes in a syringe and you just put a thin bead on the back of the lead and press onto the glass .
I did loads during the summer on a lot of new work i picked up , i noticted the lead was coming off before i started and pointed this out so first job was to re-stick the lead then call back a few days later to clean the windows .
using wfp ive never noticed any lead lifting .
trad can be a pain when you catch a jagged edge of the lead on a scrim and it pulls away from the glass .