I've done some shutter cleaning and range finder adjustment on mine, but I've never attempted a full cleaning and adjustment on this one for fear of getting in over my head. However, these cameras are not as hard to work on as some others of the same era, and there are competent repairmen around who can get the job done. A very large number of Ia and IIa cameras were sold in the 1950's, so the cameras can be had for very reasonable prices in spite of their high quality. The most vulnerable parts are the frame advance spring and the shutter cocking rack. Those parts are interchangeable between the Ia and IIa models, and not terribly difficult to find.
In the unlikely event that I ever needed to choose just one camera to keep and use from my collection, this one would likely be it.
Some sample photos from the IIa:
The Retina IIa Manual is at the Butkus site.