Transmission vacuum modulator for 560SL

Dear all, 

I have problems with one 560SL: hard shifting, particularity from 3 to 4 shift, (downshift is fast and soft),  jerks from R shift to P or N.
The first check was vacuum modulator and found out it doesn't  hold the vacuum. 
560SL has transmission 722.313 with red cap modulator, by Mercedes   A1262709079. 
Unfortunately it is no more available and can not find any aftermarket substitution. 
Now the question , how important is cap color? I can see the attachment is the same, maybe compulsory adjustment for new modulator is enough 
for change with  black cap A1262709179 which is still available at Mercedes ? 
Best Regards, 
Stan