James,
these are really tiny 3mm screws and tough to find with a square head. On my car there were screws with three different lengths (see picture). The shortest two were on the outsides, the middle ones next, and both required a M3 nut with rubber washer. Then six long ones which need special rubber covered 3mm "packing nuts".
Interestingly, the part book shows only two types of square head screws (p/n 000 990 1833 & 113 990 0033) and I believe that these are the "long" and "middle" lengths screws. I am puzzled why my car had 3 types - and I am pretty sure that these are originals.
Anyway, I am surprised that you don't need to replace the packing nuts. The rubber on mine was very brittle and broke into pieces.
If you need any of the items, call Dave he has them. I have only a few 3mm nuts and rubber washers left that I can offer.
Alfred
1966 blue 230SL automatic