The reason abbasi sb implies on going to 3S is not just qualification, its also due to knowledge base. About a month ago I was contacted via this website by a user in islamabad who has some version of a mercedes with the little v6, I think it was the 2.4 litre one.
anyways long story short - the reason was to procure intake manifold gaskets - I thought about it really hard because the intake gaskets are available easily - then came the real story.
The owner's mechanic did the "desi tune up" - he removed the throttle body and washed it (somewhat acceptable) and sealed it up with bathroom sealant RTV (bad) - then he further disassembled the whole intake manifold and washed it with petrol and yanked out a little pipe that is part of the vacuum chamber inside the manifold. This guy was looking for the gasket that goes between the two halves of the intake manifold.
Sadly - they dont exist as service parts, the gasket becomes a plastic like material when cured after assembly for the first time and remains sealed up its entire life. The manifold is cast magnesium and has an array of flaps and runners that make the elastic torque of the engine.
Point is that.
No matter how much stupid the mechanics at the MB dealer (shnwz ltd) are - they would have never disassembled the manifold - because they have the knowledge base to refer to. So no matter if its 3S or independant mechanic - the person should atleast study the machine data first.
end was that he had to buy a working condition used manifold (his car was OK to begin with - he just thought it would be a good idea to have a general toon up)