Dremel multi max tool: speed control out of whack

Hi, I've had a Dremel multi max tool for a few years, purchased from HomeDepot for $100. It's the kind with the vibrating head that cuts wood/metal/grout etc depending on the attachment you put on. The vibration speed is contro lled by a wheel that you can select from 0 to 10 (slow-to-fast). But latel y the wheel doesn't seem to work right and it speeds up and down of its own accord.
Has anyone experienced the same with theirs? Does anyone know of a reasonable fix, or is it considered a cheap tool and time to buy a new one?
Experienced opinions and advice greatly appreciated. Regards, Theodore
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On Sunday, December 27, 2015 at 10:25:37 PM UTC-5, snipped-for-privacy@yahoo.com wrote :

ut etc depending on the attachment you put on. The vibration speed is cont rolled by a wheel that you can select from 0 to 10 (slow-to-fast). But lat ely the wheel doesn't seem to work right and it speeds up and down of its o wn accord.

Can the case be opened? If so, I'd try blowing out the area around the spee d control. Maybe you could even blow it out without opening it.
Could be dust build-up.
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