606 and 603 belt tensioners are the same AFIK, I would at a minimum pull the pivot block and check it's bearing for wear, or stiffness/rough movement. and yeah, I'd change the shock. I've had a spring break on me, so I recommend changing the spring as well...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!