Any thing is acceptable for leaf springs even a nice bit of beef dripping.
What ever lube you use it just needs to get between the contact points an lube them.
They could do with a leaf lube to save the rolling around on the garage floor.
Final fix, remove leaf springs, and replace with new high grade ones, before fitting new ones take them apart and carefully file the rub points for each leaf so there are no catch points soak in in oil bath for 24 hours, reassemble packing with a hydrophobic grease ( i would recommend Lucas Red n Tacky), then carefully wrap in leaf spring tape and then coat with grease based sealant to protect and refit. Then forget for 10 years. (this is the Rolls Royce approach)
