I am going to use 10-50 Sikolene Pro S10 from Oilman. Propper Synthetic.
You will struggle to find genuine synthetic in any normal shop.
Give oilman a call and have a chat, they will explain hydro cracked synthetic is just fancy mineral oil and ester based is the real stuff.
If you buy 25l from him it works out cheaper than Mobil 1 too (which is a fake synthetic!)