So why are the cable outers grease filled when new?
Is grease oil? By all means, inject SP41 into your cables – it’ll probably last longer than oil – but eventually it’ll dry out and gum up, or, in a split system, collect dust too. Then it’ll have to be replenished or rinsed out, or the cable replaced.
Properly installed cables do not need lubrication to work properly and perform well. There is certainly a minor short-term advantage to having lubrication inside a cable system; but that will be offset by a steady decline in performance and, in some instances, a shorter lifespan of cable outers. My philosophy is ‘why bother?’. Do a good install with decent cables and performance will be constant – never any need to ‘refresh’.