SQL Question: Need to display 2 or more different Advisors from same table for each ID.

I need to pull distinct BMW Customers (which is around 5000) from Cars table and then see if these Customers have two or more different Advisors from Advisors Table ( this has millions of records), if so display those records. Customers with SAME Advisors appearing once or more than once  should NOT display. and also it should display the count of Advisors . One more thing format of Custid's is different in both tables. I tried something had poor performance and worked for small test data but not for huge Voulmes of real data. Below is query.  Please Advice? Thanks!

Output:
CustID          AdvisorName            Account              CountofAdvisors
12                  Brad                            XX                          2
12                  Brad                            YY                          2
12                  Ellen                            ZX                          2  
13                  Polly                           XX                           3
13                  Matt                           tt                             3
13                  Sally                           ll                              3

Query that I tried, doesn't give correct output: (maybe I need to fetch Custid's separately from Cars table first)
SELECT custid, advisor, account
  FROM (SELECT a.custid,
                   a.advisor,
                   a.account,
                   COUNT (DISTINCT advisor) OVER (PARTITION BY a.custid) flg
              FROM Customer_Advisors a, customer_cars b
             WHERE     a.custid =TO_NUMBER (REGEXP_REPLACE ( b.custid,'[^0-9]'))
                   AND b.car = 'BMW')
 WHERE flg <> 1;