One problem related to manifold/header/muffler/tail pipe has been reported for the 2008 Toyota Highlander. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2008 Toyota Highlander based on all problems reported for the 2008 Highlander.
Engine began revving upon acceleration from a stop light. Engine warning light came on indicating low oil pressure. Pulled into auto repair shop who found dipstick was dry. Poured oil into engine only to see it leaking out from below passenger side. Car was then towed to local Toyota dealer. Dealer replaced oil cooler hose 15767-31010 which had failed with 15767-31020 (all metal assembly). Replaced oil and restarted engine. Engine is making tapping sound and dealer recommends full replacement. Depending on option, cost is between $7500 for a used Toyota engine to $8300 for jarco engine (which I believe is rebuilt). This occurred in south carolina while we were vacationing from maryland. Thankfully, we were not on the highway when this occurred. Will have to leave vehicle here for repair and fly back to drive it home later. Btw, the single pipe oil hose was replaced in may 2010 under the ssc 90k recall at 33k miles. That is not the part that failed. This is the dual manifold rubber hose that Toyota has now replaced with an all metallic assembly. As far as I know, this part was never recalled, but there is a TSB 02011-11 available.