If you are unsure of the makeup of the cable you may squirt something inert dwn into it like silicone lube.
The days of lube fittings found in cables have long disappeared ..
If you apply petroleum products to some materials, it will attack them.

 

If it is not a sheathed cable, then this is your stuff to use. I've used this over several decades of bike cables..

My current cables are teflon sheathed, and require very little lube...

https://www.grainger.com/product/TRI...ubricant-2PB97

 

Isn't the business end of the cable inside the primary case and subject to the primary case oil? If so, it would seem that the same oil would work for the rest of the cable...

 

I bought Bike cable lube on Amazon works great..

 

As I under stand it ,, use some thing like a 100% silicone lubricant , reasons are , won't stiffen up or stick in colder weather and wont collect micro dust as bad ,
I just snagged my beloveds treadmill belt lube to do my 3 cables , got a little messy wasted a bunch , throttle much better and when I get the trans back together I expect the clutch to be at least a little smother

 

If you want to make your clutch action "smoother," then yes, cable spray lube may help. CycleGear has the spray lube & the lubing adapter for cable ends. This works.
Next, if you would like to REDUCE your clutch pull effort by 40%, without reducing lockup force, then check Burley EZ boy reduced clutch pull device. They work so well, you'll wonder why HD doesn't put them in as stock from Milwaukee. $25 all day long.

 

Actually the "business end" of the cable is in the right side transmission case cover. Loosen the cable at the adjustment in front of the engine, remove cable end from handle, drop some oil/lube in the housing, put back together and make the adjustment. I like to do this at the end of the day, and let the oil/lube work it's way down overnight. That's me letting gravity do the work.

 

 

WD40 is not a lube. Get some specific cable lube.