The black stuff on the filter is probably carbon from a less than healthy filter on a compressor. The chances are good you also have a fair amount of carbon inside the regulator as well. The green spots of corrosion are another indicator that you want to have someone take a look inside the regulator.
And I agree, if a tech goes to the trouble of dissassembling a regulator, it only makes sense to install new parts. Part of it (a large part) is liability, but part of it (the part that leads to the liability) is that parts that are working together inside a reg all have certain orientations and working relationships with each other and once they are broken in and are familiar with each other, dissasembly screws that all up and this can cause problems.
For example, all high pressure seats develop a seating groove within a short period of time by the action of the orifice against the seat. It is not uncommon, due to normal machining tolerances in the piston or orifice for this groove to be very slighty off center on the seat. So if you dissassemble the regulator, the odds are that you will not get the parts reinstalled in the exact same orientation with the result that a new seating groove will form that overlaps the old one. These two grooves will overlap in two spots and a slight leak will occur in each of these spots which will result in intermediate pressure creep.
So personally, if I dissassemble a first stage for any reason, it gets an annual service kit installed.