I coulda swore I've seen this item in the FFG books somewhere?!

I think in Rogue Trader - tho not the main book

Basically its an aerosol spray a character can use to seal a damaged void suit...

Any ideas?

Morbid

The only references I can find of it are pg. 141 of Rogue Trader Core Rulebook where a "seal patching kit" is mentioned in the entry for Selenite-Pattern Void Suits and the "Hull Sealant Spray-Gel" from the Shipboard Emergency Kit (though that is for sealing vents or bulkheads and not void suits).

Then why ask here?

Probably because it pertains to one of his Dark Heresy 2nd edition games and he's looking for a version that exists in said line. Would be my best guess <shrug>.

My players go for an (appropriately blessed) roll of Admech-issue duct tape.