@Proud Kraut: thanks for the link. I had indeed seen that one, though it's a bit different as it has (as you mentioned) shoulderboards still on, but also has the VM-style ranks, and not the BM.
@Steve and Sprogcollector:
I do indeed agree as this being pre-unification at least. It is made in 1990, and was acquired by the seller (so he states) in 1991. So it would be "mostly pre-unification", and been worn only a very short period post-unification. Is there any info on whether it is indeed true that the last units of the former VM (in their VM-organisation, not yet part of the BM I believe) were dissolved in 1991?
Excluding Handelsmarine and WSP I think is wise in this case.
Sprogcollector, I understand the last bit. In the DDR-section, others think that NOT all officers received new uniforms (I, personally, do not know how many officers went over from one to another anyways).
What the seller said would make sense as long as the officer would not have been taken into the BM (with a sort of 'contract' untill 1991) fully, but only worked during the unification. It would make sense that he used his old uniform for this relatively short period, but also changed the ranks on it...
At least, that's what I think