Hi Morpheu, hi folks.
When you choose 3DS in the pull down list of the import window, click on the "Options" button. Choose a unit that will cause a scaling up when importing. For example, if the model is in millimeters, import as centimeters or even meters. This will scale the model up by 10 or 1000. Then, the small facets shall close unless they are very tiny on the original model.
If it seems to work OK when in SU, scale down the whole model by the corresponding factor of 0.1 or 0.001. Notice that SU will not accept 0.001 as a scale factor. For such a factor, you must proceed in two steps like 0.1 and then 0.01 or the reverse.
Otherwise, you can repair probably all missing faces in one operation with the following procedure:
1 - Select all.
2 - Scale using a sufficient scale factor. Try 100 first.
3 - Use the Menu Tool --> Utilities --> Create Face This shall close all faces that where not, provided that their perimeter is coplanar.
4 - Since everything shall still be selected, scale down by 100 (use a scale factor of 0.01.
Just ideas.