I have heard of dealers doing this as well, but if you had your oil done at a jiffy lube or something like that, they probably didnt even have your filter in stock and didnt even take a look at it. I think you can buy 4 OEM filters on ebay for like $25 or something like that. pick some up and take one in with you next time

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2002 4.6is Dinan S2
Titanium Silver/Black Alcantara

DINAN
Stage 4 Engine Software
Automatic Transmission Software
High FlowThrottle Body
Free Flow Exhaust
Cold Air Intake System
High Flow Air Mass Meter
OTHER
CCFL Angel Eyes
Stealth XM Radio in ashtray : FM Mod
Pilot H3 Fog Bulbs
Cleared Headlights: Hi/Lo Beams
Hardwired Radar Detector
IN PROGRESS
Powerstop C/D Rotors: (on backorder)
W/EBC Red Stuff (F)
W/Axxis Deluxe (R)
Dice Ipod: Aux Input for XM
THINKING
SMG II
MK4
Bluetooth