Material based solutions I've come across to fix Decal stretching in Unreal 4.
Get the Material graphs free here: https://ronanmahon-art.gitbook.io/dec...
Decal Designer, now available on the Unreal Marketplace:
https://www.unrealengine.com/marketpl...
Some of the projection types only work with access to the scene texture world normal, so not suitable for decals which write to normal.