William Gleason, the short-stop, is a native of (St. Louis), 27 years old, and was formerly connected with the Fire Department, where he was considered second to none in point of bravery and dash. In 1872 he left the department to join the Peoria Club, having been previously a member of the Co-operative Grand Avenue Club, in which he had earned a good reputation. Gleason is one of the luckiest batters of the season, having been fortunate in hitting the ball on several occasions just where it counted.-St. Louis Globe-Democrat, October 8, 1885
This is an interesting reference to the Grand Avenue Club. The best evidence I have is that the club was founded in 1876 and Tobias, writing in 1895, stated that the club was founded in 1875. The possibility exists that this is a different club than August Solari's Grand Avenue Club but most likely the Globe just got the date wrong.
If this source is correct, and I have serious reservations about that, then this is rather significant. While I assume that players in St. Louis were being compensated to one degree or another by the late 1860's, there is no source that explicitly states this. If accurate, this would be the first source to identify a club that was compensating its players prior to 1875.
Checking The National Game, Al Spink wrote that Gleason started playing baseball with the Stocks in the 1870's, played with the Reds, and then in 1881 was playing with the independent Brown Stockings. No mention of Peoria or the Grand Avenues.
This source, naming the Grand Avenues as a co-op club in 1872, conflicts with too many other sources to be taken seriously at this time.