Distributor service need is based upon the internal and external conditions found.
One that is really nasty inside and has excessive endplay in the driveshaft needs attention. The vacuum advance also needs to be checked to determine if it actually moves and if it will hold vacuum indefinitely.
We perform distributor rebuilds here at ihon and we do have the nla vacuum advance canisters on hand, these are rebuilds we have done by a custom manufacturer and are indistinguishable from new.