Perhaps you have already looked at this site, but in case not..
The Southern Campaign Revolutionary War Pensions and Rosters is at www.revwarapps.org
Unlike my previous visits there, the site is operating very slowly, so allow it time to come up and to find your searches.
One pension application -- www.revwarapps.org/s42312.htm
-- mentions a Virginian John Slaughter. His military unit appears to be from Culpeper County. Whether that necessarily distinguishing the person of that record from the one you are looking for isn't known to me.
Perhaps the details you will find at the site will check back to information you already have. The Culpeper John had a brother James.
If you make a significant connection, the next step might be to go to the Heritage Quest website to see the original docments. I get access to HQ through my local library's home page. Don't know what your access might be.
Max Snead (loads of York-New Kent-Hanover-Louisa-Fluvanna-Albemarle-Amherst-Nelsons Sneads/Sneeds)
Good luck with your search.