ARC D-115 ..need advice

My D-115 has been sitting for a while because I'm not sure what do next. It originally came with the great Phillips 6550's. They lasted about 5 years. Bought a used set of GE 6550's from ARC that lasted about the same amount of time. Sounded almost as good as the originals.

The Phillips tubes are shot and can't be reused. Most of the GE's test out fine on my old Hickock tube tester.

Is it possible to find GE's? What would the cost be? Since there are 8 power tubes, would it be possible to match the set by buying just one or two tubes?

What if I decide or have to buy some of the newer versions available? Any recommendations? Most folks on this forum don't say much good about Sovteks, preferring the Tesla or Svetlana tubes. I remember the original reviews of the Sovteks were favorable, however. Who are the best and most reasonable in terms of price of dealers to contact? KT-88's or 6550's?

Sometimes, when the tubes go, they also take out a resistor in the same channel. If I need to go to a dealer who repairs ARC products, do they generally let you bring in your tubes when rebiaising and repairing or do they insist on staying with the high priced ARC stuff that they order? Who are good dealers to work with in the Midwest?

One final question, which tubes have better reliability and longevity?

Any assistance would be most appreciated. I'm currently using an acceptable Dyna ST 70 that was modified by John Hillig. Although it's a good little amp, it really belongs in a second system, compared to the great sound put out by the D-115.

Sorry for all the questions. I want to make the next step the right one, so my amp doesn't have to sit on the shelf too much longer. Yet, I don't want to spend an exorbitant amount of money.