Leak from a vaillant VCWGB221H combi bioler?

I have a leak from LH side of the boiler near the d h w. heat exchanger i think, it is plastic black 3 tubed chamber to the left of my boiler.
model numbers vcw gb 221 h (gc 4704414).
I believe the plastic DHW HE is now replaced with a kit.
As i have no manuals, what is the new kit, and what other mods is required if i replace it with new kit?
As everything is working OK, what are consequences if the leak unattended.
I am really not sure what some threads on the forum talk about TRV's, PCB links, and Div Valve disc.
Any advice/comments appreciated plz in advance.

macaroon
January 2009