Ideal W CF 450 leak between heat exchangers

[Rideaux]

On a 35 year old very good condition Ideal W CF450 (GC 41 407 51)

The top two of the 4 joints between the two halves of the cast iron heat exchangers are weeping when the boiler is warming up. - no leak at all when cold or hot
Question:- anyone know what type of seals are used between both halves of the heat exchangers ?? Or got any diagrams ?
Just want to keep it going for a few more months - have tried Fernox leak sealer F4 which did help a bit but still loosing half a cup of water each cold start up
Thanks

 

[ShaunCorbs]

Sorry but new boiler time not designed to be user serviceable

 

[PETE 123]

I may be wrong but 30 yrs ago a friend replaced the o rings between two parts and leak stopped.