strange alterntor or water pump problem

[courtney]

car is a 1999 e300td 200,000 miles

2.5 years/45,000 miles ago water pump was replaced- no problems since

2--3 months ago the alternator went out/pulley broke and was replaced with a bosch alternator that appears to be the right part and match the mercedes one

a week ago the fan clutch bolt unscrewed itself and the clutch and fan fell down in front of the radiator
bolt was not broken, scracthed or anything -VERY WEIRD

nothing was hurt, they put the fan clutch back in and 2 days later the bolt backed out again and messed up a bunch of stuff

the new alternator we got was clutched and the consensus was that it needed a none clutched one
there is a lot on the forums about clucthed vs non clutched alternators on this model of car
but i could not come up with a consensus on which one it should have

thinking the alternator was the wrong one i went to mercedes used the vin number and got one there, the parts/shape/numers etc match and the one from mercedes has a clutch also

so we are stumped
they want to put the car back together with loctite on the bolt and see what it does, i still think something is wrong but i dont know what
the replaced alternator seems to be fine, pulley seems fine

but something seems to be stopping/jerking the belt and backing out that bolt


never seen anything like this on any of my cars
any input about alternator issues /pulley issues etc would be great