Exactly same issue/fault on my Baxi 105e Combi.
I can confirm is two screws on my 105e, threw me for a while that one!
I have also replaced both diaphragm kits presuming a split to be the cause of the leak and it now seems to be worse! Not to proud of myself there.
Leak is dripping from the join of the hot water Pressure Differential Valve and the the Diverter Manifold. Seems to emanate from within the diverter manifold itself.
Losing all pressure on the heating circuit so definitely coming from there. Must be some internal seal or 'gate' either corroded or not closing properly which is allowing the leak.
I am not a boiler engineer but I can't believe that joint is intended to be water tight? It seems to be a mechanical join intended to align the rods that push each other.
There is no compression seal or washers there, the parts simply engage and are secured by the two grub screws gripping the flange/collar of the join. Can't believe that was ever intended to be water tight?
If anyone knows the answer do post please. May need to call a plumber to this one, will post solution here if I crack it.
Neil - Rayleigh
February 2009