I had the alt pulley rub on the bottom hose on my 1980 300d after I tightened the fan belt. It only rubbed when it idled rough when cold. it took about a week before it failed. When I put the new hose on , I twisted it slightly so it was always at least 1" from the pulley. It only happened because the belt adjustment was at its limit.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

There ya go.

OP, another possibility......the tensioner pulley on the serpentine belt may be losing tension.

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'06 E320 CDI
'17 Corvette Stingray Vert

Still leaking here... I think it now comw from the water pump... Is there a way to rebuild those od the whole unit need to be replaced?
Cheers.
Olivier

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E300TD year 2000. RUSTY SOLD
cost a fortune to maintain on the road
but run well on WVO
Second Merc died due to corrosion ( NOT rust) How can mercedes get away with that for so long?
Third lasted a month then went away...
Fourth now... Corroded too...

it was the water pump as well, it as been changed yesterday and no more leaks, so far...

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E300TD year 2000. RUSTY SOLD
cost a fortune to maintain on the road
but run well on WVO
Second Merc died due to corrosion ( NOT rust) How can mercedes get away with that for so long?
Third lasted a month then went away...
Fourth now... Corroded too...