Updating Oracle database from SQL Server as linked table

I have a medical records system where parts live in Oracle and parts
live in SQL Server. I'm trying to inactivate a lot of patients who
haven't been seen since the conversion by updating them on the SQL
Server side and then updating the Oracle side to match. I'd like to be
able to use the following query:

UPDATE server..user.table
    SET OraField1 = 'I'
    WHERE OraField1 = 'A'
         AND OraField2 IN (
            SELECT SQLfield2
                FROM SQLTable
                WHERE SQLField1 = 1
            )

However, when I do this, I get an error saying that the field "was
re****ted to have a DBTYPE of 130 at compile time and 5 at run time".
This appears to mean that there's a field on the Oracle side that was
defined as Number without any precision information. How can I rewrite
this query to actually work? OpenQuery doesn't seem like it will do
what I want, and I don't want to accidentally inactivate everyone in
the database...

Thanks!