Many moons ago when I used to own a comic and collectible store I used to use the services of a very nice woman named Susan from The Restoration Lab in Boston. Although she primarily works with comics she used to be willing to work with other types of paper material. Prices were very reasonable back then but I have not had use for her services in over 10 years so cannot say for current work and prices. When I was using her for work though it was excellent every time with good turn around. You may want to give her a try as the damage to your sheet is not very different than the damage seen on many comics with the exception of the tar that is.
Their website is -
http://www.therestorationlab.com/
If they are not interested in tackling it, Comic restoration people are a decent avenue to look into as they often deal with many different types of paper restoration issues and if they are good can handle just about everything.