Not sure about that, the Merc manifold is hard plastic. Caustic soda is very nasty stuff - you could try making a small quantity in a bucket & chucking various bits/types of scrap metal into it to see which it attacks. Unfortunately, I suspect Aluminium is one of them.......
I can (from experience) say that I tried various fuel cleaner products with limited success but when I tried FuelTone for the first time, I put it in my dad's Passat TDi 130 which had, over the years, become rather smokey with a smell of diesel hanging around. It came to MOT time & I added this a week before (to a full tank) & drove it about in various modes (from cruising to thrashing). I noticed it gradually getting better & better until there was virtually no smoke visible! When I took it for the MOT, it passed the emissions test with the lowest figures it had ever had (0.0something)!
It is
not an every tank requirement but worth doing it on a monthly basis. I use it on the diesel (Land Rover/Mercedes) & the petrol Cars (Audi/Mercedes/Kia) that myself & the rest of the family have. I'm the designated mechanic for
all of them...........

I reckon it's the best value I ever had from a product so definitely recommend it. You can get it on ebay.