Only way to tell is to take the tensioner off. If it doesn't return to the normal untensioned position, it's bad and must be replaced.

The roller comes with the tensioner, I believe, so you might as well replace the tensioner to avoid hassles (such as being unable to tension the belt with the old tensioner).

Peter

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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!