Hi; I have a JD 990 compact tractor and recently had a throw out bearing failure. When we were doing the tear down I noticed that there are vent screens located on the sides of the bell housing that appear to me that they would allow moisture and dirt to get into the housing. Presume that they are to allow for pressure relief or heat reduction but not sure how or why either of these issue would develop. Any ideas? How about replacing them with solid covers to eliminate contamination? Any thoughts?