I'm going to jump in with some oblique ideas.

If you are using the MS OLEDB provider, you may not realize that it has not been upgraded past 8.x and probably never will be because Oracle won't provide critical info to MS anymore. So, MS now suggests that a linked Oracle server should be provided by the OraOLEDB provider. It goies without saying that the version should be at least the same level as the target server. To use this, however, the Oracle client must be installed on the same machine as SS.

Another idea of possible interest:

Perhaps you could create synonyms in a sql server database (hosted in the same SS instance) that point to the linked Oracle server. These can be views which means that they can preprocess some of the Oracle sourced data before presenting it to Excel.