Help with gas boiler
 

Gas boiler developed a leak (drip) it is a Baxi 100HE plus
I believe it is coming from the heat exchanger manifold (google)
The part it leaks from is a plastic drain plug, it was tight but an
eighth turn appears to have stopped it for now.
My concern is if it leaks again further tightening may cause damage to
the drain plug, if that happens how important is the drain plug? If I
damage it am I likely to get much water dripping? and What is the
purpose of it as I have never used it for `draining` in the last 6 years.

Image below:

https://imgur.com/a/jujZq

On another note I noticed from google that there is a condensate trap
hidden behind the combustion box door panel (not the main outer cover)
should this be periodically cleaned out? Again never done in 6 years.