high mileage oils?

I just use a good premium motor oil and a factory filter. 'High-Mileage' is a common marketing ploy that sure sounds pretty. Synthetic motor oil blends may offer some advantages in heavy-duty/high-temperature applications.
Are you having valve seal issues? What engine?

I plan to run Shell Rotella T in my rebuilt 360-turned-408 stroker, because of the hydraulic flat tappet cam and no-roller-anything. Modern conventional oils lack the heavy metals that helped lubricate those high-pressure bearing surfaces, and I wiped a cam lobe on the old engine in the car because of that.

If an engine is all-roller, I don't expect it to be as big of a problem.

yes valve seal issues on an 89 318 tbi. burning some oil look like just on the left side of the engine. just some blue on the left exhaust side

Start with a quality motor oil. HDEO is a good oil. I wouldn't go higher viscosity than 10W-40, I see some people go 20W-50 to slow oil consumption instead of servicing the engine.
Do a dry/wet compression test to make sure that the rings are ok.
Valve seals are fairly easy to do on a 318. Hand tools, a simple valve spring compressor and compressed air to hold the valves up during the operation one cylinder at a time. You may find hardened rubber exhaust valve seals from the heat.

i just did an oil change on mine and I used Penzoil High Mileage 5-30. It didn't seem to hurt it at all and i have some blue out my exhaust too.