James,
Prior to doing anything that requires a large monetary outlay, try
changing the oil, and use 20/50.
Yep, she has a lot of miles, but the 10/40 may be the problem at the
moment.
The problem with these Vanagons is, a guy winds up being so buried in
them, after a period of time, and then there's the sentimental value,
what in the heck does one do?

Get more buried in it with a new engine for $2400.00, (Labor extra) or
let all the money he has invested sit and rot?

A definite diminishing value call---

What's a 83 Vanagon GL going for      nowaday's?

This a very personal thing, and your going to have to make a LARGE
decision, on you own on this one.

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Terry 85 GL