Note; Radiator Sealant is different from Block Sealant.

Radiator Sealant often has particles of stuff that circulate through the Coolant system to block off holes.

Block Sealant often uses something called generically Water Glass (don't remember the real name.)
You need to read the makers instructions but typically with Block Sealant you get all the Coolant out of the Engine and Flush several Times with Water. You add the Block Sealant according to the Instructions and run it according to the Instructions. After that the Water is drained out and you let the Engine sit to dry out something like overnight before adding the Coolant/Water mix.
On the Internet I have read to run the Engine for a longer amount of time with the Block Sealer in it; the claim is that that works better.
Most Block Sealers have a money back guarantee.
I doubt if Mercedes wants people using them.

I have read some articles that say to keep the Block Sealant out of the Heater Core when you use it.

The Radiator Stop Leak often as stuff they bill as Water Pump Lube and particles of stuff to block the holes. You mostly just dump them into the Coolant.

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84 300D, 82 Volvo 244Gl Diesel