If the central locking is working via the interior switch, then it’s fair to assume that the problem is only with the exterior lock mechanism. About then, a locksmith will go looking for a faulty or deceased door actuator switch or mechanism, as this is often the cause of this condition.

But it could be a case of dirty or dry electrical contacts on the mechanism in question, too, so don’t rule that out as a first (and cheapest) possibility.

Failed axle seals in Toyotas of this vintage are not unknown, but I’m not sure that they’re any more common than in any other make or model. And you’re right, replacing the seals in this model requires an awfully big hydraulic press and some pretty specific tolerances to be observed.

But the bigger question is why the seals keep failing and, more specifically, why two seals would fail simultaneously. Often, an axle seal will fail because of wear or play in the wheel bearing it helps protect. But to have two to fail together (one being a new-ish one) suggests a problem with the rear axle’s breather system. This is designed to allow pressure to escape as the axle unit heats up and internal pressures rise. If the breather isn’t allowing this to happen, the pressure can increase to the point where it will cause the seals to fail. So that’s where I’d start looking. A blocked breather fitting or crimped breather tube could easily be the cause.

It’s pretty unlikely that a 1987 Toyota van even has a limp-home mode. These were pretty simple engines and shouldn’t really tax a good mechanic too badly. Provided you have spark, fuel and compression, an old Toyota four-cylinder engine is more or less obliged to run.

If you’re happy that the carburettor and ignition are spot on, the next step is to perform a compression test to see if the engine is internally worn out. This is a possibility and would explain the sluggish performance. You should also make sure things like the air filter and fuel filter are clean and not restricting the flow of fuel.