Possible explanations:
1) You can't get replacement parts to service a bike that old.
2) They don't want the liability if the whole frame is toast
3) They're all younger than the bike and don't know how to work on it
4) Being unequipped to work on a bike that old, they'd rather not do the work than do a substandard job.
5) Or you could simply believe whatever they told you when they turned down the work.
FWIW, I used to drive a 30 yr old Volvo. Great car. Loved it. But Volvo dealers wouldn't touch it. I had to find a vintage Volvo shop who specialized in the older models, knew how to work on them, and had a supply of the necessary parts and tools.
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Formerly fastest rider in the grupetto, currently slowest guy in the peloton
