weber silver genesis B valve/burner question
We have a 5 year old NG Weber BBQ grill. We have noticed that the back burner doesn't fully light. We have taken it apart and as per the manual, we cleaned out the burner tubes and cleaned the spider guards. THere was no large accumulation of dirt or spider webs in the burner tubes and the spider guards were relatively clean. After all the disassembly the last burner still does not light all the way. The first and middle burners are fine, the connector bar on the left is lit, but the last burner is barely lit halfway from the LEFT. We are surmising, perhaps incorrectly, that the valve on the manifold for that burner may be clogged. How does one check and clean the valves on the manifold? Or any other suggestions?