I've devised a simple mod that appears to have overcome both of these problems. All it needs is a 16mm washer fitting between the underside of the flat bed chassis and the bogies.
Click the thumbnails for larger image
The Macaw bogie bolster.
Remove the bogie by pulling carefully
Bogie removed showing the pivot where the washer fits.
Washer in position
The washer needs to be 16mm maximum with a 7mm hole. The hole may need opening out slightly with a round file or a 7.1mm drill bit if you have one. The thickness of the washer should be 1.2mm or very slightly more.
Make sure there are no burrs on the washer and place it over the pivot stub on the chassis, replace the bogie and make sure the bogie pivots freely and does not rub on the wheel flanges. If the bogie does not pivot freely it may need rubbing down slightly on some coarse emery paper or wet and dry paper, followed by some fine to achieve a smooth finish. If the emery paper is placed on a bit of old carpet while the washer is rubbed down, the edges will be thinned more than the middle which will help to reduce friction when it is back on the wagon.
Rubbing down a washer on emery paper supported on a scrap of carpet
The washers only add 2 to 3 grams to each wagon but it certainly helps to stop derailments. If you want to add more weight, you can remove the factory fitted weight that is fitted between the top and bottom parts of the flatbed and replace it with lead. It won't make a big difference but every little helps
