Most of guys who bought KTM TPI from first production they had this problem with leaking oil tanks. I also had leaking oil tank on my EXC250 TPI but after replacing it with UPDATED version of tank that problem is fixed for me, but for some guys also new tank started to leak. I think its just bad quality of plastics and very weak point for bolts.
I also found on some KTM TPI bikes the rear mount for this tank was welded not straight, so that also can cause tank to crack because one bolt is holding more than other one. Soon i will do video about KTM TPI PROBLEMS & HOW TO FIX IT so also this will be covered in that video.