Header tank leak - Pulsa Coil 3

I have noticed that the water level has started dropping in the header tank requiring topping up more frequently than usual, also there is a sign of water leaking around the top of the main tank near the join with the header tank. Is a leak possible here and could one fix it with Radweld or similar?

Don't think it will work.
Could try leak sealer for heating systems.
Repair / replace to top tank?
Mike

Chances are that the 3/4" fiber washer that seals the joint is on it's last legs and tightening it up will make it break apart,for the time it takes (less than an hour) I would empty the top fill tank with whatever small containers you can find and a sponge, undo the 2 connections to the main tank, clean up the connections and replace the 2x 3/4" fiber washers then reconnect and fill to correct level.