I had a quart of "synthetic", don't remember the brand, and used it in my truck. As it came out there was a glob, at the end. I had it for at least ten years.
Not many "synthetics" are true synthetics now. They are just more highly refined dyno oil.
true Synthetics are available but not widely stocked, here, in the states.
I use Mobil One but soon as I get a little more urge I'm going to locate a true synthetic for the little Mercedes, at least.
The Ester based synthetics are way more stabile and slicker than owl ----.
When they first came out I ran it in a Plymouth with a 440. I had to tighten and replace gaskets on the engine as it seeped through everywhere. It did help power and it cleaned up the engine better thaan kerosene, not that it wasn't spotlessly maintained.