As a professional Mercedes technician for 31 years I have to disagree with some of the information here.
I have never had to modify any brake pads in any way, shape or form and would caution anyone against suggesting that others do so without knowing the competence or experience of that person. Brakes are critical to safety and should not be messed around with unless you are absolutely sure that you know what you are doing. Now, I accept that there is generally a high level of competence amongst posters here, but that does not mean that all readers should be encouraged to modify their brakes without ensuring that that advice clearly includes a strong element of caution lest someone goes plastering anti-squeal grease over the friction surface of the pad. Believe me, I've seen it done..
Obviously, if you are a professional or an experienced driver/engineer you are free to choose your own pads as you desire and indeed you may find some alternative set-up that is to your preferance.
I ALWAYS fit genuine Mercedes pads supplied by the dealer. I have tried using pads from the same manufacturer like Pagid or Textar but I can tell from the feel of the brakes if the vehicle is fitted with genuine pads or not and am not prepared to experiment with customers cars or indeed their safety and indeed the pads are not expensive anyway.
If the pad is a tight fit in the caliper it is more likely to be corrosion or contamination on the caliper that is the problem, not the pad itself.
Brake squeal is caused by high frequency vibration and the function of anti-squeal grease is to damp that vibration.
I do not work exclusively on old Mercedes, but have never had a problem with a 113 with sqealing brakes that wasn't cured by normal good practice. I have had a couple of later cars (202 chassis) where I've had to change apparently good discs in order to eliminate brake squeal and it's entirely possible that this may be required on a 113, never say never!
Incidentally, braking performance can be significantly improved on many occasions by replacing old but apparently good discs with new ones., even if there are no visible signs of defect. I learnt this in my race car driving days....