High Mileage Oil?
 

Any strong opinions on using HM oils like Castrol GTX High Mileage or Havoline High Mileage Synthetic Blend in an older LR2? For the sake of discussion, assume that high mileage is 75K+ miles.

I've used the synthetic Castrol GTX in my Disco 2 V8 at 90K miles. It's a good oil.

Any premium synthetic oil usually is a good investment if you plan on keeping your vehicle for a long time. They all contain additives to recondition seals, etc. I personally use Amsoil but it's pricey and not as accessible as other comparable brands.

Regular changes and a premium synthetic will go a long way to help an aged engine but remember to factor in a rebuild at some point after 100,000 miles.

My 200Tdi likes a 20/50 mineral oil changed every 3,000 miles, just the way it is.

I would hope the Volvo engine would last well over 200K with proper Mx.

As to high mileage oil...

It has additives which expand, or "bulk up" the valve guides, creating a closer fit and reducing oil consumption.

I wouldn't use it until you start seeing significant oil consumption. Once you start using it, keep using it. If you use it and the switch back, the valve guides will leak even more since they are now worn in with the increased bulk from the additives. They'll lose the extra bulk if you remove the additives.

I'm not aware of any other drawback or benefit to high mileage oil. It might also prevent or minimize leaks from engine block seals.

Synthetic reasoning
 

In winter synthetic is the difference of your engine spinning fast enough to fire up or going .. noo,noo,no.,click, click! from thicker viscosity non synthetic . I've run it for a couple decades w no problems. Castrol or Quaker State.