Michael,

Interesting that the parts guy didn't know about a flame trap....naturally aspirated Volvos have had flame traps for decades!...Hell, Volvo invented the flame trap! Both my 240 and 850 share the same type...and yes, if they are allowed to get fouled, back pressure builds resulting in seals and gaskets failing. There have been some reported dealerships that have been removing the little plastic trap with the thinking that they are more trouble then they are worth. Good argument, but the whole point of the trap is to eliminate the risk of fire (ie:flame trap) in the event of a severe back fire igniting gases. Overkill? maybe, but IMHO I would leave it in place, and just make a point of checking it and cleaning it periodically.