Hi - the issue in front transfer case; the box where the driveline to rear separates: The box has five bolts. There are two sizes of holes for those bolts: 12 mm and 10 mm. Should the larger holes have a guides or not?

The box was removed at dealer's workshop to change the leaking seal at 130.000 km. Now - 140.000 kms it has been separated again and dealer says that some of the holes are worn to 12 mm; and they ask 4.000 eur/usd to replace it. No way; it can be fixed with 500 eur/usd. But I am curious, that did they forgot the guide tubes there at first place, or what has caused the leaking. The bolts were loosened by itself.