Should I ??? '82 300SD knocking

[smitherz]

I found this ad and would consider this at $500 he wants.

"For sale a 1982 Mercedes 300SD Turbo Diesel with about 240k miles. European headlights, chrome Mercedes rims, chrome trim, sheepskin seat covers, sunroof, etc.... Car runs but makes a knocking sound and am told it probably needs a new engine. I am selling this as a parts car or it can be repaired. I was told this could be done for around $1,700. Asking $500 obo. Lowered price because I need to have the car sold by the end of the week. Car is sold as is."

I have not looked at it yet... afraid I will buy it without asking.

opinions?
Scott