there may be nothing wrong with your springs at all.
Say for instance that the vehicle has a spring rate of 180lb/inch on each spring, then by loading the vehicle with , say a 180 lb driver, the load will be taken by the RHS F&R coil springs, 90lbs each (for sake of argument) and the vehicle will sag on the rhs a shade under 1/2" (because the driver is not sitting exactly over the line between the two springs) . If you have loaded the vehicle heavily on the RHS then of course it will sag on that side.
One of the benefits of the later model RR EAS airspring is that the EAS ECU detects this and compensates to level the vehicle.
The Classic as I remember it has relatively soft, long travel variable rate springs, so an initial heavy enough static load will take up the "softer" compression element and compress maybe 1". However, double the load and it may only deflect say an additional 1/2" because of the increasing spring rate ... hope this makes sense
Mind you, with age and heavy use, coil springs do develop metal fatigue and ultimately sag. You can either replace the springs (preferably with a matched set) or get your own springs "reset"...which requires them to be heat treated and possibly re-wound..
MY99 RR P38 HSE 4.6 (Thor) gone (to Tasmania)
2020 Subaru Impreza S ('SWMBO's Express' )
2023 Ineos Grenadier Trialmaster (diesel)
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