HH-66 vinyl glue. My can is slightly gassed out, almost as strong a bond as Locktite Vinyl Fabric Adhesive as viewed at Wal/HDepot but not as strong as an old half gone Vynabond tube.

Recommendations for adding a solvent, the partly missing evaporated solvent ?

The MSDS for the HH-66 thinner is at:
http://www.rochfordsupply.com/tech_docs/HH-66%20Thinner%20MSDS.pdf

Like the MSDS for the glue, it indicates a mixture of toluene, acetone and methylethylketone(MEK) as the solvent.

If you can find the HH-66 thinner, that might be the simplest. Solvents are nasty, toluene particularly so, IMO.