Here's the thing, though: Since stainless-steel lines don't bulge as they age, and since the inner Teflon lining is hidden behind thebraid, there's no easy way to inspect the lines for warning signs of imminent failure. This is no big deal on a race car, since the lines are (or should be) replaced at least once a season. On a street car, where most people are likely to let YEARS go by without even looking at their lines, it can be an issue

You know guys, just so we all are on the same page, stainless steel brake lines mean that there is a stainless steel braid over a plastic or rubber tube. The lines that the brake fluid is in are not stainless steel. The theory is that if the braid is tight enough, it reduces the amount of swelling that occurs from the brake fluid pressurizing when the brakes are applied. The lines cannot be solid stainless steel because they need to move with the suspension. If your soft pedal is because of the stock line swelling from the application of the brake pressure, the stainless steel sheathed line might help somewhat. Is there a downside? You can't see the actual tubing that carries the fluid so you can't see any possible cracks or ageing. There are also instances where if the braid is not done correctly and any of the stainless steel "fibers" get unraveled, they will dig into (and through) the inner tube very easily. As far as a stainless steel sheathed line being more resistant to air intrusion than the stock line, it doesn't happen. The sheath is neither gas nor liquid tight, only the inner tube which is very similar to the stock tube. Some people change to stainless steel sheathed lines and say it is a difference of night and day (however you are also going to have to bleed the lines and top up the fluid which can also make a big difference) and some people change to the stainless steel sheathed lines and don't feel any difference at all. But the mechanics behind what the line is doing is pretty straight forward.