Yes time will eventually catch up to your baby Cummins, but for now your oil consumption sounds about right for it. Towards the end of its life it will usually leak more than it consumes! A replacement B5.9 runs about $6500-8k. There are a lot of places that sell rebuilt B5.9's. But.. best bet is to talk to a Cummins dealer first before looking for merely a cheap price. Jasper rebuilds as Rich mentioned are a decent engine. One fellow I know bought one from Advance, and had major problems with it after it was installed, in the form of heaps of oil coming out of it's breather hose. It had to be swapped out under warranty for free, but cost him a lot of downtime. So if you aren't getting the engine from someone Cummins recommends or a reputable rebuilder, beware.
Although the B5.9 engines in most straight trucks is similar to that in the Dodge pickups, they ARE NOT identical, and cannot be swapped!
Things that are or can be different include accessory bracket drillings and mounts, oil pans, manifolds, flywheels, air brake compressor, power steering pump, etc.
You will need a replacement B5.9 for your specific truck in other words, so best to find out from Cummins or the truck manufacturer exactly what you have before getting price quotes.
Hope this helps and doesn't complicate things, but if you take time to shop around for what you need before the engine goes, you'll save yourself a lot of downtime and grief.
-Weave-
