Looking for recommendations to replace spark plugs, 104,000 Km on veh, should the coil be replaced also ??
That equates to around 60k miles so you have another 40k to go before they need changing.
Iridium are the originals if I remember correctly. 
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I thought iridium were good for 100,000Klms and Platinum for the 100,000 miles? Leave the coils, theres 8 of them.
Here’s the various specs:
Spark Plug
NGK PFR5G 11E : Normally Aspirated
NGK PFR6G 13E : Supercharged
Plug Gap
0.039 - 0.043 : Normally Aspirated
0.047 - 0.051 : Supercharged
Torque
25 - 29 Nm : Spark Plug
4 - 6 Nm : Coil
4 - 6 Nm : Cover
With torque settings, the lower figure is for previously used fittings, the higher one is for new. New plugs therefore go to 29 Nm but used Coil and Cover bolts go to 4 Nm.
If the seals need replacing, there’s a US vehicle has the same set at much lower cost than Jaguar parts. I think it’s the Lincoln LS. Others will be able to confirm.
I’m not a fan of dielectric grease and prefer clean contacts but that’s just opinion and you’ll find as many for using it as you will against.
The car has platinum or iridium plugs from the factory that are rated for 100K miles. They really can last that long unless they were fouled for some reason. These generally run in the $10-$12 neighborhood apiece.
I just saw yesterday a revue regarding NGK plugs, the guy purchased a set from Amazon dirt cheap there were subtle differences between the plugs but there was one that was obvious and that was the diametre of the centre electrode, much thicker on the bogus one;