Newby with d24 engine problem

[Fmark]

I am presently living in Victoria Beach, NS and have owned a 1984 VW LT 28D Camper for approx. 10 years approx 200,000 km before rebuild
Last year while travelling on a 10 day trip, my timing belt broke and destroyed the camshaft and damaged a number of valves.
After having it towed back home, the head was inspected and I decided to order a new cylinder head from Germany plus gaskets, new water pump, new belts new head bolts and the 6 injectors rebuilt with new parts.
A local mechanic (with a little assistance from me) put the engine back together and after doing the timing and bleeding the injectors the engine started and ran quieter and with more power for about 10 hours at highway speed. Then I heard a dramatic increase in sounds coming from the engine and accompanied by a significant reduction in power. Also, there was a noticeable increase in black / carbon smoke coming from the exhaust system especially when climbing hills. I was able to limp home with the machine.
Also, I had topped off coolant, done an oil change and had just replaced the air filter.
The mechanic is presently checking the following
Air filter and intake flow---OK
rechecking timing
checking compression of each cylinder
stethoscoped the rebuilt injectors---OK

ps--- there is a small amount of oil around the vacuum pump and there is a hole in the side of the pump where it appears that a plug has popped out and there is a small amount of gases/oil coming out of it.
I don't know if there is anything from this component that would affect/ cause the engine problems described

Can anyone give me a solution for this problem
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