Dave,
I have two of those silos:  18x60 and a 20x80.  The small one was put up in 1976 and is now on its second pole.  The big one was put up in 1986 and is still on the original pole.  For the most part, we just weld new attachment points onto the pole and change the chains every few years.  Replace the bolts at the bottom of the pole when replacing the chains.  Keep the bearings greased (we had to replace one).  The flying dutchman is MUCH cheaper to maintain than the Harvestores.  They work great for corn silage, but tend to be too slow for haylage unless you cut really short.