Opel Automatic Box Year 98 Motor 1.8

Dear All.
I have doubts about the maintenance of my vectra. A mechanic tells me that the box carries a filter and another does not, and we must change the oil that is already bad.
I change the TPS, oxygen sensor and I find that he spends fed up but you have to consider that it has the exit very slow and you have to accelerate more than it common to start moving. I imagine that it is the box for the theme of the oil itself.

Can anyone guide me?
Thanks in advance

If you carry a filter, you have to change it because it is saturated and sometimes it is useless to clean it.