Den der har riktig spec, så den kan du trygt bruke. Det medgår som du har nevnt rundt 1.2 liter.
Det er også et filter i beholderen som anbefales og byttes, har selv aldri utført dette, men til info

Kan være at denne kan kjøpes hos Møller.
https://parts.vw.com/p/Volkswagen__/Oil ... 2385A.html
Delenummer. 431-422-385-A
Også brukt hos Mercedes, delenummer; 0002360055.
https://www.yoyopart.com/oem/13441222/m ... 50200.html
Så det skal nok fint la seg oppdrive.
Viscosity and temp performance are fine, but the PS fluid may attack the rack seals. In many older vehicles, this was the case. It is something that would take some time and exposure, so flushing now would probably avoid damage.
There is a filter disc in the reservoir (see Bentley p.48.7). It should also be replaced when you flush out the system.
To get the old fluid out, I would first drain out as much fluid as possible, refill and pressurise with clean ATF, and drain that again. After that I would replace the filter and refill again with clean ATF. The whole system capacity is 1.3 qts., so you're not talking about a huge amount of oil to do a double flush. The correct ATF is Dexron, not FLM.
Be careful while doing this to never run the engine with a dry pump. Vane-impeller pumps must be filled with fluid or they will gall and be damaged very quickly.
Undo both banjo fittings at the pump and lower them so they drain. Also undo the return line where the rubber hose from the reservoir attaches to the hardline at the right of the engine bay and lower it. Take off the pump belt, and spin the pump by hand to help empty it.
Undo both fittings at the steering rack pinion valve housing. Lower the lines so they drain. Work the steering from stop to stop several times, as it will force fluid out of the open fitting ports. You could elevate the rear of the van to drain more fluid out of the long lines.
Seal everything back up and fill the pump reservoir with clean ATF. Replace the belt. Start the motor very briefly and stop it. Refill the reservoir. Do this several times until the fluid level doesn't drop after a quick start/stop (no more than 2-3 seconds running). To air-purge the system, idle the motor while cranking the steering stop to stop at least 3 cycles. Always keep fluid in the reservoir."
One drain/refill may be enough, if you feel that you got most of the fluid out, but if you want to be sure, then repeat the drain/refill and purge.