Protective 'sealant' on rear plastic panel

Good morning,
Please see photos below.
While cleaning the van yesterday I noticed that there is a strip of black 'sealant' that has come loose from the rear plastic panel on the passenger side.
The 'sealant' is only on the left side vertical edge (looking at the van with the cab to the left)
I describe this as 'sealant' as I am unsure if this is a factory fitted proper seal that has perished, a factory applied bead of silicone sealant or a DIY bead of sealant applied by a previous owner.
Your help to clarify what this is and how to replace it would be appreciated.
If it is a DIY silicone bead I am a bit worried about making a mess if I try to replace this.
Cheers
Rob
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You're lucky that yours is black. Mine's light grey and it oozes out whenever we get some hottish weather.
Mine is like a mastic and I scrape it off with something plastic so's not to scratch the paint but it reappears at the next hot spell.
Had the van since 2002 and it has done this since we bought it. There must be an endless supply behind there!
I think it is to stop the panel from vibrating - rather than sealing anything.

Frank

Cheers Frank for the usual quick response. I thought it is odd that this only appears on one edge of the panel.

Lucky you! Mine appears at the front and rear edges and along the bottom of the panels.
Someone must have been in a generous mood when they made my van. Or using up the last of the light grey before changing to black?

Frank

I have got, or did have, black silicone around the plastic panels. Over the years long strands have appeared and I just pulled them off like bootlaces.

I must get round to resealing one day!

PB