Lawrence,
Most of the items on your list are normal conditions and look like a wish list for a shop that that is looking to boost sales. Virtually all 17 year old diesel engines have a small oil leak somewhere, so if it does not leave oil drops where you park and you never have to add oil between changes, its not an issue that needs to be repaired. All belts wear and all mufflers rust, so installing a new belt and muffler that show no signs of failure is a waste of money. All differentials make some noise, so what kind of noise and how loud? The brakes on your coach are probably original, and will probably out last you, so why replace them now?
Now we are down to the only things on your list that might be an issue, the shocks and surge tank. I would have both of them checked by a shop that you trust. The term "shocks beginning to leak" is questionable to me because shocks are the most oversold item in the service industry. Do you have any ride control issues? Last the sure tank, if it is leaking it will get worse, so where is the leak? If it is a loose clamp or fitting, tighten it, but if it is a crack in the tank, replace it soon.
Gerald