A suggestion..
Maybe look to standard neoprene flexible pressure pneumatic tube. "Flexible" is a relative term. They are smooth, and hard-walled enough to use those "push-in and seal" fittings that can hold quite high air pressures. If your oil line pressures get above about 15bar, then you have to resort to metal, like brake hydraulic tubing, but I don't think lubrication norms get anywhere near so high.
Size-wise, I have used them as 6mm, 8mm, and 10mm.
You might be going for similar sized in inches, like 1/4" or 3/8". There may be places which need thinner.
Neoprenes are immune to oils and most solvents, and you can even get them in various colours + black.