Hydraulic clutch fluid

Today I was replacing the clutch master cylinder on my '66 D200, and as long as I was doing that I figured on replacing the slave, too. Then a buddy, who is a heavy equipment mechanic, stops by and says that as long as I'm into the system this far I should consider filling the system with a light hydraulic oil instead of the normal brake fluid. Reasons being: it's not subjected to possible overheating like brake systems are, and it doesn't tend to absorb moisture like brake fluid... Well, I'm pretty set in my ways, already had brake fluid for it, and figured that is what the system was designed for and the factory specifies; so that's what I used. But it got me thinking- does his suggestion actually have some merit? What other positives and or negatives would there be to following his suggestion?