The imports accounted for 21.9pc of all used-car sales last year: up from 20.6pc the previous year, the report claims.
And so far this year the experts say they are witnessing similar buying trends.
Driving the import surge are perceptions of much wider choice and value for money.
Much of the focus to date has been on such buying patterns diverting people from purchasing new cars.
But it is only natural that such buying is also diluting the total number of originally Irish registered motors that change hands each year.
These new figures certainly bear that out.
According to vehicle history and data expert Cartell.ie, the number of used 'Irish' cars (as opposed to imports) being sold has been falling for a few years now.
More accurately it has been noticeable since really big numbers of imports have hit the market.
The findings emerge from the latest 'trends' analysis by Cartell in conjunction with BAC Auto Consulting.
It means, for example, that used 'Irish' car sales for the first two months of 2019 are already down 6,765 - a decline of 3.8pc.
The rise in used imports last year was a contributory factor to this, the report says. And so is the fact that a lot of new cars were registered before the onset of WLTP emission data last September.
They were then sold as used (or 'newsed') the following month. That sent sales up 8.8pc in October over the corresponding period for 2017. But it still wasn't enough to avert an overall decline in volumes as sales fell in eight of the 12 months.
Last year was down 1.8pc compared with 2017 which itself was 1.8pc lower than 2016
In 2016 there was a peak of 945,000 used 'Irish' cars sold. Since then there have been those year-on-year falls of 1.8pc.
The report says: "There is little to inspire confidence that anything but a continuation of that decline with used-car sales expected to be down around 3.5pc for the full year."
