Only main problem with brake fluid is the absorbing of water. As the pipes heat and cool the internals drip moisture, as brake fluid is a good absorber of water. * note on fluid container, unsealed can absorbs moisture. Regular bleeding, bi-annual, at all bleed points pushes the moisture out and prevents the seal leaks and soft pedals. Sure you can go 80,000 without touching fluid, but, how much corrosion is in the system from the moisture? Like the rusty master cylinder bowls. I, myself, would rather know I can stop, rather than hope I can. I have cars from the 50s, 60, 70s and newer, and all are bled every 2 years, no matter what, Same as cooling systems. Another story. As for lead additive. Been a mechanic for 52 yrs., never used the additive, never saw a street problem without it. The 50s to early 60s cars were run on white gas (as it was called) non-lead fuel. Lead was introduce in early 60s ( note fuel price increase for the additive) the eliminated in the 70s ( another price increase to leave it out). Unless you race a car or drive it hard you don't need it. Like the Jags, they used hardened seats because of the racing by the factory and just put them in all the XK engines ( might get an argument here ) but, my good machine shop noted that the Brits knew about hardening steel and said it is not needed. I drove a Triumph GT6 hard for 200,000 miles with only a burnt valve, not a seat problem. My XK engines are driven, not cuddled, and still not problems, except the carboning from todays fuels.