I think you did the right thing. It could be bit's of old hose or it could be the diaphragm deteriorating... As to it putting in alot of advance it can do that(28 deg does seem like quite a lot!) but remember you are not under load, so even @ 2500 you're vacuum can be quite high. In other words, when under load like driving the transmission and wheels and moving the weight of the car you have to open the throttle(carb butterfly) much further to reach and maintain the same rpm as when sitting in park in the driveway. Also, I'm pretty sure it's a smaller allen key than that. You found that @ 2500 you are getting 20 deg of mechanical. Most likely the weights in the dizzy are either 13L or 15L, dbl that to get 26 or 30 deg mechanical. So @ 2500 w/ only 20 deg mech you are not "all in" yet. This is where a recurve comes in, to bring the mechanical advance all in at a more optimum time.