The 200 series through 1985 seem to be prone to this failure. I published a safety warning on these distribution blocks several years ago in Rolling. It is not necessary to have a 240 pound pedal pusher to suffer the failure. Normally, the blocking valve in these blocks does not move - and in those systems that have not been flushed every two years (I suspect that this includes most Volvos from the 80s), the corrosion builds up in the cylinder bore. Then the first time that the piston moves a little, the corrosion cuts the seals and the leak starts - could be very small or relativeloy significant. You may not even notice it, and the piston may not move enough to trip the brake warning light. However, the result is that fluid can leak from BOTH circuits of the dual triangular system with no warning light, and you can suffer a total brake failure!! In the year that I published this article (sorry, I don't remember which issue it was) we had at least three members with this failure, and two of them were driving when they had a total brake failure. Since that time, Volvo has recommended regular brake system flushes, and they have changed the brake distribution blocks - they are no longer made of iron, but are alloy and the corrosion problem should be much less.

The way to check them is simply to unplug the sensor wire and unscrew the plastic switch from the block. ANY evidence of fluid in the sensor cavity means replacement of the block. It simply is not worth risking brake failure!

As noted, this is also a very good reason to flush the brakes on a regular schedule and use a pressure bleeder like the Eezibleed or the Power Bleed