If you running windows 10 use 3d Builder ( some builds have dropped it but you can still download for free through Microsoft Store) it has auto repair on opening STL and OBJ files - it was built on NETFABB which Autodesk bought - Microsoft then pealed some of the repair out tools out of NETFABB and built into the 3d Builder I use it all the time as quick cleanup tool it will heal most files with problems.