I searched I found a few posts & videos but none for X308.

Since The issue is intermittent, It may be difficult for a shop to troubleshoot.

Mostly happens on cold start. I smell a gasoline smell in the cabin which dissipates in a minute when I drive off with sunroof opened at angle.
When I start again, after car sitting only 15-30 minutes, no smell.

Are there common causes to explain these symptoms? My 2000XJ8 has no cabin filter. Which is hard to believe.

I assume there is a leak & fuel gasses are released in the engine bay & make their way into the cabin.

 

Don't be surprised you don't have a cabin filter. N/A models didn't until '02 I believe?

For your gas smell, before your cold start, I would pop the hood and turn the key forward to just before starting it. Leave it so the fuel pump stays engaged, go look and smell around for fuel residue. Be sure to look all along the intake and fuel rail, peak in around the injectors with a flashlight and throttle body, be sure to look under the car and on the ground. Since fuel dissipates quite quickly, move as fast as possible. Also check back toward the fuel filter area.

If you find nothing, fire it up and repeat your check.

 

I did the checks. Car had sat overnight.
1st I opened the hood. I looked with flashlight & smelled. I did smell a fuel smell from the passenger side, which was surprising but, saw no leak.

Next w/o sitting in the cabin, I turned ignition to on & quickly checked the engine & no change in smell. Again I could see no leak.

Finally, I sat down & started engine & quickly moved to examine engine.
Again saw nothing. I was looking with the flashlight towards the hoses under the engine cover closest to windshield/firewall.

I will probably eventually have to take it in to an Indy shop.

 

You may also want to get the fuel pressure checked. Too much fuel pressure is a slim possibility and a sign of a possible fuel pump going out.

Keep checking, you never know when you might catch a leak.

 

I’m the original owner & replaced the fuel pump December 2012 @ ~ 65K miles. Now have ~ 93K miles.

I will ask the shop to check the fuel pressure when I eventually bring it in for this issue.

Thanks!