Both of them leak a bit . Is there an O Ring / I can repalce ? Or do I have to replace the entire sensor/solenoid ?

 

They are standard lip seals, part # AJ8-2856, approx $5.00 -$10.00 each

Jaguar Valve Seal, LH Cam Cover, All V-8 - AJ8-2856

https://www.partsgeek.com/gbproducts/DC/602-05627671.html?utm_content=DN&utm_term=1998-2009+Jaguar+XJ8+Variable+Timing+Solenoid+Seal+APA% 2FURO+Parts+98-09+Jaguar+Variable+Timing+Solenoid+Seal+2004+1999& utm_source=google&utm_medium=ff&utm_campaign=Parts Geek+Google+Base&gclid=EAIaIQobChMIq_jSor6L2gIVBJR-Ch1L4w_sEAQYBSABEgJfCPD_BwE&ad=47433948012



https://www.ebay.com/itm/VVT-Seal-on-Valve-Camshaft-Cover-for-Jaguar-Two-Pieces-AJ82856/361515845827?epid=670301025&hash=item542c0608c3:g: v0kAAOSwxp9W77G~&vxp=mtr



Easier to replace them with the valve cover off, but you can replace them in place.

 

Welcome Paul, please introduce yourself in the New Members Forum...top left task bar, Forums, General Jaguar Forums, New Member Area and tell us about your car also.

As for your issue, seems CK has already helped out...nice. Here's a pdf on the VVT http://www.jagrepair.com/images/Trai...ual-9-5-01.pdf ...the VVT description starts on page 103.
Here's a screen shot from that describing the process of the VVT.