To Seal or not to Seal

My 30yr old Weil McClain boiler now has two small leak but am not ready to replace without some research. The oil company said they can put in a sealer that may last for a while but a plumber told me that it leaves a residue in the pipes and can cause problems with the coil when a new system is installed. Opinions?

sealer is almost always a waste of time and money. 30 years old, time for it to go. Look into a Buderus