930 guys are quite motivated to clean CIS injectors - RoW 930 injectors list for $120 each for Bosch OEM. Or $200 each for the Porsche part..
CIS injector cleaning
Many shops are geared toward EFI injectors and don't want anything to do with cleaning CIS injectors. Might have more luck with shops that handle diesel injectors. If the spring is broken/weak, nothing anyone can do. If the internal screen is clogged, well, maybe you can clear it without breaking the screen. If the spray pattern is bad? Meh.
Those that will try to clean them want $20 per injector to start - eg:
https://www.jaguarfuelinjectorservice.com/CIS%20Injector%20Cleaning%20Testing%20Service.htm.
A complete set - of new SC injectors - from our host, with seals, will run you $213:
Porsche 911 CIS Fuel Injector Kit with Bosch Fuel Injectors with Seals
$269 for for all of the above, plus new sleeves & o-rings:
Porsche 911 CIS Fuel Injector Kit with Bosch Fuel Injectors with Seals and Injector Sleeves with O-Rings
It's not had to cobble together a CIS test rig; if crack pressure is within spec/match (the springs get old/weak), they still seal and don't dribble or leak under pressure, they flow at the correct rate/within 10% of all your other injectors
and the spray pattern is good, there's probably not a lot of point trying to clean them.
IME, you might find that cleaning them can improve the spray pattern slightly on one or two that were perhaps a little iffy, any that were junk when you started are still junk - and the ones that were good are pretty much exactly the same...