theres a very good reason that leaded lights leak when they are cleaned with wfp and dont leak with the trad scrim and polish
its the method of construction, the lead or the canes as they are called are cut and soldered to fit the glass, if it was fitted like this the windows would be draughty and leak
so they fill the joints with wax by waxing the panes and scrubbing wax into the canes sealing all the gaps
with the trad method of damp scrim and a polish the canes are kept flat against the glass and the dirt layer that embeds into and protects the wax is left undisturbed
the problem with using wfp is its strengths are its weakness in this case, im not going to go into a commentry on how wfp works, if you use it you dont need me to explain it to you but wfp is a very effective cleaning method, too effective for leaded lights, over a period of time the protective wax is removed and the windows fail
many owners of period properties choose the extra expense of buying and maintaining such a property for the pleasure of living there, they also consider thems custodians rather than owners
the cost of refurbishing these windows is high , so a niche market is created if you have the nouse to take advantage and charge accordingly
you could raise £1 a window to £5 or more per window with the right marketing
alternatively you can wait til the experts are called int to restore the glass and provide evidence that the damage was caused by wfp
its up to you, but I know how I have approached this and didnt need to share it with you