'97 V70r no blower/demist air to windscreen

[Yog Sothoth]

OK, first up, this is not a problem at the moment but it seems a good time to sort it before autumn and winter roll around.
The blower system on my P1 V70r works just fine (apart from the air con which needs sorting but that's another kettle of fish). It blows cold or warm air from all its vents as it should, powerfully. Apart from the windscreen vents that is.
If I set the controls to blow onto the windscreen only, with all the other vents closed, and the blower turned up full, all I get is a faint zephyr emerging from the windscreen vents, the merest breath of air, not the blast I would expect. I can hear the blower motor whirring away and if I open any other cabin vents it blows a gale.
If I have a misted windscreen in winter, it takes ages, 5-10 minutes or more, to demist.
I suspect there's some air deflector somewhere which diverts air where needed, depending on the set of the controls, and that something is jammed or seized, preventing the 'windscreen' setting from actuating.
I checked online, RobertDIY etc and can't find anything relevant. So, do any of you fine folks have knowledge of these problems? Can I get to the blower unit and wiggle the plastic baffles, oil the actuators and hopefully enable my windscreen blower setting, before I need it!?
One thing I do wish these cars had is an electrically heated windcreen. I'm surprised they don't, as my Ford Scorpios of similar vintage did.

[Derek UK]

https://www.youtube.com/watch?v=MhBzo9TUaBI&t=191s
Usually motors available on the Bay.