Calipers for my 1974 Corvette S.B. Vert rear calipers are leakng

I thought everyone had gone to SS lined calipers.  All the aftermarket suppliers only sell SS calipers.

"Lined" or entire calipers SS?"  I would think perhaps the lined ones are rebuilt, and "IF" totally SS, they are brandy new! 

Lined.  I believe they rebuild the cores that you send in. Plus I think I read years ago that someone was making new castings. 

I've never heard of a totally stainless steel caliper.

I've read and heard various pros and cons of O-Ring callipers, but in my own experience, I'd never think of anything else now.

Back in the 90's it seemed we were changing callipers every month due to leaks, etc and we definitely had to bleed the callipers each year due to air in the system.    Eventually, I bought 4 new Stainless Steel lined, O-Ring callipers from Ecklers.  And I never looked back!    While I think its a good idea to bleed the system annually, it doesn't need it now.  The braking performance is better and I have more confidence in them.

With regard to S/S liners, I notice that there are in fact some callipers on the market that use O-Rings, but not S/S liners - the rational apparently being that S/S adds a lot of cost, and that the O-Ring design alleviates some of the need due to better sealing.   

Therre is nothing wrong with lip seals, but the o ring seals are better.   If the car is driven every day, not much difference.  Most of our cars are not.   Stainless sleeves are also better.

If you are inclined one of the best things you can do is bleed the brakes annually, flushing out all the old fluid.  Regular brake fluid has an affinity for moisture and will absorb it.  this happens gradually even in a sealed system.  little used lip seals are worse for this.  If the brakes are used often enough, even a few good pumps on the pedal will do, they maintain a better seal.  With o ring seals this is not necessary.  The moisture in the fluid is what causes detriment of all fluid contact components.  That is what causes the fluid to change color.  

This can be avoided by using silicone brake fluid but I do not recommend it.  Silicone has an affinity to absorb air making it difficult to bleed.  More importantly it has a lower boiling point.  This can cause brake fade in an extreme heat situation.  IF the car is stored most of the time or driven like an average car its fine.  I like to push mine once in a while.  Stainless steel sleeves help stop corrosion which in turn damages either type of seal. 

With a bit of research it is easy to find rebuild calipers with sleeves and o rings.  I have actually bought them at Autozone in the past.  Much cheaper but have worked well on my car.