I have a 54 in. JD walkbehind with a 17 hp KW engine that I`m having starter problems with. I replaced the key switch,cleaned all the connections and it worked fine for a while but the problem is like my mother-in-law (back). This mower also has a new battery. Sometimes I can go out to my shop and turn the key and it will fire right up and sometimes the selinoid on the starter just clicks. I can tap the starter and sometimes it will fire. Brushes in the starter bad???? Any ideas????