From the restoration of WPK38
The leaf springs were replaced in 2012 and then, having settled, taken apart and treated:
Each leaf was sanded then polished smooth before applying a coat of satin epoxy paint. Next they were coated each side with a thin smear of nimonic anti-seize lubricant. Finally a 1mm strip of high density polyethylene (HDPE) was inserted between each leaf.
The net result is that the leaves move easily against each other which when working in conjunction with adjustable shock absorbers provide a far more compliant and controlled rear suspension.
Custom leather gaiters — an original option — keep the grit out and the lubrication in.
This passage also appears in the brakes and suspension chapter.
What the factory said
Gary Grant, quoting the factory literature on the Jag-lovers XK forum, notes that the maintenance chart in the XK140 Operating Handbook calls for the rear springs to be greased periodically through the fittings on the gaiters, while the XK140 Supplement advises spraying them with penetrating oil. Check the interval against your own handbook. On a car without gaiters, jacking the rear so the axle hangs lets the leaves part slightly and the oil work in.
Source: Jag-lovers XK forum, “[xk] greasing the springs” (Gary Grant, 2014).
Fitting new springs
New springs carry more curve than old settled ones, so eye-to-eye they measure shorter and may not line up with the shackle at first. Christopher Potempa, on the Jag-lovers XK forum, describes this as normal, recommends renewing springs in pairs even when only one leaf is broken, and suggests polishing the leaf faces while they are apart — the same principle as the treatment above.
Source: Jag-lovers XK forum, “Fitting Rear Springs” (2021).