EDIT 25th of april.

It is not where I thought it to be...it is the exhaust gasket failing. Called the mechanic, he said they replaced it with a homecut one which can handle up to 250°C. Is it enough? And the stuff is hard to cut, so maybe a wrong cut? 

Is there a quicksolve? 

Still have the questions about all the in- and outlets on the heatexchanger, so keeping the ol message below..
Added two vids where I found the leak. 

TIA,

Wouter 

Hi,

I have a problem with soot at the pump and engine neer the heatexchanger. 

Last year I had the heatexchanger fixed. The exhaustpipe too. But now I peeked and saw one site full of soot. I have no problem with Heater or exhaust. Manifold is full. 

Where could the soot come from? I thought that there shouldn't be any exhaust gas there. But this seems to defy this thought. 
Or is there an easy other explanation and dito fix? 
I have uploaded picture and video on WeTransfer
https://we.tl/b-UyWefsrmNh
TIA

Wouter 
M-35 engine.