Drivers window

[Robblucky]

Hi folks

Today I was changing door barrel on my 1996 mk 5 transit smiley ambulance 2.5 diesel twin rear wheels to do this I had to remove window and manual!! regulator there is a piece about 8" long which the bottom of the glass sits in anyone no what it's called? been trying to source one on internet the old one disintegrated in my hand......any help really appreciated.
One more thing the ambulance has a cube back made of fiberglass any ideas on the paint to use for this?
Anyone interested on seeing photo of her in her hey day just type in p58 gcm to google.