Baxi 105e combi - leak

I have a leak at the back of the dhw pressure differential valve, i changed the dhw pressure valve but it looks like it is leaking from a gland on the brass manifold where the dhw pressure differential valve connects with the spring clip. It only leaks when the running the hot water. Can this gland be changed or will i need to replace the whole manifold. Also can anyone tell me the part no. for the gland, if it is available on it's own?

Thanks.

Spring clip?

There's a spring clip on the bypass pipe, right at the back, item 99.
Just an O ring in there, Item 100, baxi 248018

Although the diagram is not exactly the same as mine it is the area between 101 and 102 that is leaking.

sorry chris my mistake did nt say its a 105e instant