Because there are situations in which {HEAD ~ a bearing assembly} is not exposed to {TAIL ~ contaminants}, a bearing seal may not be needed 
is not exposed to
Because there are situations in which { HEAD ~ a bearing assembly } is not exposed to { TAIL ~ contaminants } , a bearing seal may not be needed
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH