Low oil presure after driving for a while

I don't do the mileage to make that sensible and the 15W40 behaves all year round.
It's only Rob Parry wanted to put 20w50 in it.

 

Always used 20w50 in our Type 4
Even after the refresh. I accept the downside may be the odd clattery hydraulic tappet not pumping up quite so quickly as the oil is a tad thicker when cold but I just don't get on with the thinner stuff.
For me the most important thing has always been to change oil and filter every 3k miles.
I know they currently recommend 400,000 miles between services , but call me old fashioned...

 

Interestingly the addition of an oil pressure gauge on the T3 shows me when the oil is degrading (that was when it had the 2.1 wbx). I used 20w50 in that as well with zero issues but you can actually see pressure dropping off as the oil gets older.

Now it's got the Tdi it uses oil with gold plated globules in it that costs a fortune...progress

 

Call you sensible, those attractive long service intervals are designed to see the car through it's warranty, after that - do one.
The same was true in the 70's, so that Type-4, 5,000 mile one must be suspect too.