Air Filter NJA3558AA OEM
What about NJA3558AAX?
https://www.sngbarratt.com/us/#!/Eng...b-73f8a8cba0bb

SNG Barratt listed as part type: Standard $20.80
They have the NJA3558AA listed as part type: Standard $54.67
They have the aftermarket listed for $16.00 listed as part type: Aftermarket & part number “NJA3558AA*”
I know the Jaguar brand (whoever makes it for Jaguar) part # is NJA3558AA

SNG usually is clear with part type & identifies aftermarket but, in this case they do not seem to distinguish between NJA3558AA & NJA3558AAX, listing both as “Standard.”
I wonder of the NJA3558AA @ $54.67 is the only Genuine Jaguar filter & the NJA3558AAX is actually an aftermarket filter despite also being listed as “Standard?”

Over the many years I’ve had my 2000 XJ8, I had used both Genuine & Aftermarket air filters & holding then side by side, I once saw the aftermarket one was very slightly shorter. I think this may have caused a whistling noise at high speeds, not sure. Since then I have overpaid for the Genuine filter. I usually change ~ 10K miles. I know service manual says do every 30K miles but , somewhat dusty in Phoenix.