I had all the intentions of sorting my golf headlamps towards the end of last year, my research (including a screamingly genuine youtube review) lead me to buying the Meguiers Headlamp restoration Kit but you need to lacquer them after restoring to retain the UV protection and the lack of any...
You can also insert a very thin screwdriver or the end of a penknife blade for example in the slot and twist it a little to widen it slightly to help it off the terminal.
When lead is stored in damp conditions prior to installation it can cause degradation of the surface. Not sure this is what's happening here but it might be.
Apologies, it wasn't aimed at you Ronnie, hence you don't need to get over anything, we know you you clearly understand the concept. ;) My post was aimed (poorly) at anyone thinking otherwise.