How to fix a leak between the burner and heat exchanger?

A problem has been identified by an engineer on my 10 year old Isar HE30. It had a L F fault code which could not be reset. When the engineer removed the front cover he explained that condensate was leaking from the gasket between the burner and the heat exchanger. He said that this was dangerous as gases would be leaking out as well. He condemmed the boiler and capped of the gas supply. He left without anypossible remedial work apart from a new boiler. Was his diagnosis correct or was he just "pulling my chain"