The issue of inadequate/close-to-none zinc content in modern-spec oils, for older-type engines such as the XJ 4.0, with flat-tappet cams.....was discussed in a recent thread here on the forums.
IF you do wish to supplement, I have three recent, sealed extra bottles of 'ZDDPlus' additive available.
Summit lists it for $15.95 per bottle, plus shipping:
http://www.summitracing.com/parts/CRO-86092/
-----> $27.50 shipped, for the three.
IF you do wish to supplement, I have three recent, sealed extra bottles of 'ZDDPlus' additive available.
Summit lists it for $15.95 per bottle, plus shipping:
http://www.summitracing.com/parts/CRO-86092/
-----> $27.50 shipped, for the three.