The key here is safety, first and foremost-
You car car is a 1987 model, 16 years old.
If your caliper is not leaking and all that you want to do is to replace the torn dust boot/seal, then you do not need to use compressed air and take the piston out.
It is your determination whether the piston and its seal are in good condition: No scoring, rust or damage, not to mention leaks or any other reason that your brakes would not perform properly.
Please understand, I feel very cautious about advising people on safety items.
If you have any concerns or don't feel you can perfrom this repair yourself, safely, have a professional do it for you.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)