Has anyone ever done this? The ones on my Alphard have dried up and cracked (presumably from exposure to hot sunlight in Japan), so I've purchased two more. However they look like they'd be easy to break if mishandled, so if anyone's got any info/experience on changing them then I'd love to hear it.

For clarity, this is the part I'm talking about:

 

https://www.japeurocarparts.co.uk/buy-front-windscreen-glass-moulding-drip--lh-86810-2195-2122-0-d

 

There's one each side of the screen.

OK I did it anyway. Quite easy. Remove the wiper arms and take off the scuttle panel (all plastic clips that push out from underneath. Using a door card removal tool (with some kind of padding underneath the fulcum to avert any risk of scratching the screen) prise up the old mouldings. The fasteners will break when you do this so you will need to carefully pick out the broken bits from the retaining clips or you will not be able to fit the new mouldings.  I cleaned up the area under the mouldings and scuttle panel and applied a little ACF50. There's no need to do this but it made me happy! The little bit of lubrication also made it easier for the new mouldings to press into the retaining clips. Press the new mouldings into place. Replace scuttle panel and wipers. Job done.

Are they a tight fit or do they rattle at the bottom like mine do lol?

They are a very snug fit. No movement at all.

great stuff!

Hi do you have any pictures of how to do this?