Jammer- Welcome to Autopia!
What a cool thing to find, an older Jag that still has its original paint! Most of them seem to have been repainted by now; I can only think of one XKE in our Jag club that still has the original paint.
With older single stage paints like that (my '85 Jag is ss also) I like to use a fairly old-school approach, such as a glaze topped with carnauba. IMO that gives the best "look", the one most compatible with that type of paint and the car itself.
I'm assuming you won't be exposing this car to the elements too much and that you won't be leaving it outside for extended periods. A synthetic sealant would provide great protection, but again, I just don't like how synthetics look on cars like yours.
If it were mine, I'd probably go over it one time with Meg's #80 to reduce any marring (I'm assuming it has a bit after all these years, most older Jags seem to). The #80 leaves a "Meg's glaze" effect behind, so I'd just wax over that, using something like Souveran. IMO Souveran gives a "rich" look that really compliments older cars.
In the future, I'd use some form of mild paint cleaner, then a glaze (I prefer Meg's #5, #7 can be a little tricky to use) then the Souveran. The cleaner would take care of any oxidation, the glaze would "nourish the paint" (which isn't ad-copy BS when you're talking about this older lacquer), and the Souveran would do the rest.
One of the Pinnacle "kits" with their Paintwork Cleansing Lotion and Souveran might be a good way to go.
