the wagon 83 year is w123 chasis

the engine is super DIY friendly just expensive if you do screw up bad..

they are reliable engines as long as you maintain them .. valve adjustments filter changes fluid changes etc the transmissions last long.. i have a rebuilt transmission so i want to say the original chunked at 200k maybe..

but youve got to watch out for run away diesel problems.. the p/o of my car said it ran away once.. vacuum shut off didnt work so it just didnt shut off til it burned all the diesel..

look for blow by in the engine.. to much and the engine is in need of replacemnt or rebuild

if you can take the air cleaner off and u tube.. with the engine off and keys in pocket and cold engine try and spin the turbo .. if it spins freely its good and check for shaft place.. the p/o thought the turbo was bad because my 300D was sloooow off the line .. nope turbo is fine..

look for oil leaks of course.. its an old diesel it will drip some.. get service records of course

if its a wagon check to see if the self leveling suspension works

their is more but i dont know what else