205-510D Transmission

Just picked up a Murray 38710A mower. After a carb replacement the Tecumseh 13hp runs strong. Took the slop out of the steering. The deck just needed new blades and a grease job. Only problem now is in the 205-510D transmission. I drained what little 90 weight was still in it and noticed there was a lot of fine bronze particles suspended in it. Refilled, and re-installed. Runs and shifts fine. Problem is there is a lot of play. When not running but in gear I can push it forward and backwards a couple inches. Same slop when using mower.
Can't find a replacement 205-510D so was wondering: Is there an alternative 5-speed that will bolt up to this mower? Any ideas?

205-510D Transmission