OIl companies don't always tell you if they are using esters. I like your use of high mileage-type (HM) oils since they do contain a little extra seal conditioners which might stop a leak from ever happening.
Castrol Magnatec is alleged to use polymer esters. You could buy that at walmart for cheap (great oil really) and then order LiquiMoly Motor Oil Saver, which is mostly seal conditioner, which is the main significant difference between normal oil and HM-oil.
Alternatively, my fav full-syn HM oil is "Valvoline full syn with MaxLife" as they call it, having some titanium these days too. Then, you could add a small amount of polymer ester via "HyperLube Zinc Replacement Addtive" or another ester additive such as "LubeGard BioTech" which also has lots of moly.
When you say "ester" you could be referring to the POE form, found in Ravenol brand oils from Germany (amazon or other mail order here). Or Redline has POE as well. Both of those could be converted to the High Mileage HM-type of oil by adding the aforementioned LiquiMoly Motor Oil Saver seal conditioner additive.