The more the chain is worn, the longer it is, so the more "slop" there is taken up by the tensioner.
When the tensioner bleeds down (as it does when the engine is off), the chain slaps around until you get oil pressure -- needless to say, the more slop, the more slap, and sooner or later the guide gets cracked or broken. There goes the chain, unless you are REALLY lucky.
Check the chain stretch often, it's far cheaper that doing valves.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!