I think 8500 is high with those issues. All of those problems are easy DIY on that car but I would suggest to the seller that you would have to take the car to an indie mechanic and an upholstery shop. Use them for bargaining point to get the price down to at least $6000.

The OM617 will probably never be as smooth as your OM603 but should be smoother than you describe. Ask when the last valve adjustment was done. Should be every 12 to 15 k miles. Also a DIY. The vacuum pump is normally a little rackety so don't mistake that for valve noise or rough running.

They have no pcv, just a hose from the valve cover to the air cleaner assembly. Visible oil around that connection would be a good reason to check for blow-by. Remove the oil filler cap while engine is running. It is o.k. if it does a little dance just sitting on the cover but if it flys out of your hand, there are blowby issues. Many such issues are corrected with the valve adjustment but there can be bigger problems.

Good Luck! Pix would help.