I'm not sure how to answer the question,
Any individual with a time served of refurbishing a Idler Drive will be capable of working on one in any condition. The limitation only being how much of a project they are willing to undertake. A 'Barn Find' at a few ££'s cost and in need of a total overhaul can yield a healthy uplift in value when completed, and some refurbishers relish such discoveries.
In general a Garrard Idler Drive is a very basic TT design, albeit a Vintage Design, and by some revered.
In the present day, the 301 Model has somehow been seen as a model to be reintroduced as a Marketable Item at an exuberant cost, I can see where owners of this offering as their purchased model, may have an approach to a repair service with an aloof attitude, as the Value of the item will be much more influential, for the service selected, over the adeptness of the service engineers understanding of the mechanics and electrics used for the design.