Depends on your idea of rebuilding. You'll spend more than $11,000 getting a $2,000 240K mile TD to the condition of a pampered $13,000 100K mile TD, and you won't have the resale or insurable value. The thing is, $13,000 for any 1984 300TD is a questionable use of money (unless it's John Lenon's or Elvis'). To put it in perspective, you can buy two good W124 300TDs for $13,000. Not that you would, but you really have to want that specific 300TD to pay $13,000 for it. Put in another perspective, you can get a 94 S500 with 130K miles for $13,000. Again, not that you would.

Sixto
91 300SE
87 300SDL
83 300SD