I could only access data for the first 5 months of 1998, when the VW Gol ranked #1 with over 21,000 sales each month, adding up to 119,044 units and 17.4% market share over the period. The Gol is also the best selling car in Brazil in 1999 and 2000.
The Fiat Palio is weakening a little and loses its 2nd spot to the Chevrolet Corsa Hatch in February 1998 before getting back to 20,000+ monthly sales in April and May of that year. The Chevrolet Vectra, 6th over 1997, climbs to 4th over 5 months 1998 with 32,557 sales and 4.8%, ahead of the Fiat Uno (4.4%), Ford Fiesta (3.6%) and Ford Ka (3.4%).
Full 5 months 1998 Top 20 Ranking Table below.