As alternative parts for servicing, it is worth considering fitting a washable, high flow air filter and a high spec oil filter at service time. Costs are reasonable and capital outlay on the air filter pays for itself within two or three services. Around £36 for the air filter and a competitively priced oil filter at just over £10.
For the XJR, the air filter is 33-2273 and the oil filter, HP-1014. This also fits XKR and STR models. Service wash and re-oil kits are around £13 and contain enough cleaning and oiling fluids for 5-6 cleaning sessions. To order, just go to ebay or type these part numbers directly into you search box. Do please ensure that you order the correct parts for your particular model.
I`ve used these filters for years without any problems. Quality is high and K&N are a favourite manufacturer with the sports, competition, racing and drag racing fraternities.
Personally, I can recommend this type of filtration for peace of mind installation knowing that I have fitted some of the best alternative after market parts available.