I have an 11 year old self-propelled Toro Recycler (20018). It has been a great mower, but I'm having problems. The left rear wheel locks up if I'm pushing it forward without the engine running. If I pull it backwards, the wheel spins freely. If it's running the wheel spins freely. Wondering if anyone has any suggestions? The obvious answer might be to always have it running when I'm moving it, but I have to push it thru an area with a lot of bark and it's messy and dusty to run it over the bark.