Override a access check but also pass control back to the primary controller under certain conditions?

I use a contrib controller that has a _custom_access function that I need to override.

I add a RouteSubscriber, and point the access check to my own controller. Now I want something like:

if ($condition) {
  return $new_access_decision;
}
return $original_controller->accessCheck()

so I can contrinue to rely on the original logic for most cases, and just override for a small subset of cases.

I don't know how to inject the original controller into my mine though, and if I try to add it as a paramter to the RouteSubscriber service, I get

has dependency on a non-existing service [original controller]

which I take to mean that controllers aren't services.

Inject the class_resolver as a regular service, and then call

$this->class_resolver->getInstanceFromDefinition('\Drupal\example\ExampleController');