I have several Mercedes that blowout the defrosters but barely out of center vents--is there a common fix to this? Especially 107 chassis

On the 107, there was a problem with the heater box breaking under stress. You have to remove the box and reinforce the area that is broken.

have the same problem in my SEC.It is still to scary(time consuming)to fix for me

In addition to the breakage that Benzmac mentions, there is also the problem of the vacuum actuator that is located INSIDE the HVAC box. A major bit of work to rectify.

When the first version of the ACC came out, the dealers did do a ‘courtesy’ fix when the 107s were new, but it was not an official ‘campaign’. The fix has to do with some modifications that allow more airflow through the center jets during AC operation, as the original setup had too much air coming out of the defroster vents.