Hermle is arguably the largest manufacturer of clocks and clock movements. Formally known Hermle Black Forest Clocks they've been producing clocks since 1922. What I love about Hermle movements is the ease to work on them and the availability of parts. Hermle movements have a wide range of applications with a wide variety movements. Speaking to their ease to work on their movements, mainsprings are normally one of the harder/time consuming things to work on with a clock movement. The main reason is that on most movements you have to remove one of the plates and then insert your mainspring/arbor and then go through the time consuming process of lining up all the pivots to the plate as you reassemble it.
Removing Hermle Mainsprings
With the Hermle movement all you have to do is let the mainspring down, THIS IS VERY IMPORTANT AS FAILURE TO DO SO CAN RESULT IN DAMAGE TO THE MOVEMENT OR TO YOURSELF. (sometimes you have to remove the chime hammers too depending on the movement but that is only 4 screws) and then remove the screw holding the click lock in
and then just remove the click lock, arbor and simply slide the mainspring barrel out. Replacement is in reverse order. Hermle mainspring barrels are stamped with a number (the numbers represent different size/strengths of the mainsprings) so you you simply replace the mainspring/barrel with one that has the same number. Some movements may have different sized mainsprings/barrels on the same movement so pay close attention to them as you remove them.
Here is a good link to the Hermle manual.
Another good link on cleaning the Hermle balance units.
This one will walk you through cleaning a Hermle movement.
Here is a good link for cross referencing Seth Thomas model numbers to Hermle movements.