While I have a number of ancestors who passed through Maryland, to the best of my knowledge my Flake line did not and my line was definitely in North Carolina in the 18th Century, long before the date of your great-grandfather's birth.Most of my direct lineages left Maryland too, and so I've not done a lot of research in Maryland after the 1700's and I regret that I can't really offer you much help.
I can offer a few suggestions, but that's about it.First, check out the Maryland Archives official web site.They have a lot of records which can be searched online.
Most of the reference books of which I know for Maryland - Indexes, abstracts, transcripts, etc., - almost all pertain mostly to the 18th Century and earlier.There are some out there, but most of the ones of which I'm familiar are for the earlier period.Robert Barnes does have a book of Maryland marriages which I believe would probably cover the time period of your ancestor whom you've mentioned and it is available at many major genealogy sections in public libraries.
Also, have you tried RootsWeb's message board. It is very similar to GenForum and while many researchers are found on both boards, quite a few are only found on one board, or the other.
A third web page, though not as active as either GenForum or RootsWeb, is GenCircles.Each board has it's advantages and disadvantages.
Also, have you done a search using Ancestry.Com?Many of the results to a search on Ancestry.com do require a paid membership in order to see the page where the result is to be found, but some are available to the public too.