1/2 quart every 97 miles? That is a huge oil leak.
If you're using a good quality diesel rated synthetic oil like Shell Rotella-T 5w-40 or Mobil 1 Turbo Diesel Truck 5w-40 then you can likely extend your OCI to 5000 miles.
I use the Shell Rotella-T 5w-40 and change it every 5000 miles in my E300, and every 7500 miles in my Passat TDI. (The TDI, being a direct-injection engine doesn't dump nearly as much soot into the oil, hence the longer OCI).