Never had to do it myself. Just throwing other ideas out there too.
http://www.mcmaster.com/#threaded-inserts/=bj5crvhttp://www.timesert.com/You might check if Stihl has a over sized replacement like these.
If the Standard Collar Screw is part #1127 664 2400, DG 8 thread, use Oversize Collar Screw part # 1127 664 2410, DG 9 thread, for 1127 series saws such as MS 290, MS 390
Installation: If the thread has been stripped, the damaged mounting hole in the engine housing already has the required diameter (approx. 8 mm) and does not
need to be drilled out. Coat the DG 9 thread of the new collar screw with Red LOCKTITE 262, or equivalent and apply it squarely to the bar mounting face.
Use an 8 mm stud puller to install the collar screw into the engine housing and tighten down to a torque of 16 Nm.
If the Standard Collar Screw is 1123 664 2400, DG 8, use Oversize Collar Screw 1123 664 2405, DG 9, for 1123 series saws (021, 023, 025, MS 210, MS 250). It will also work on the 1130 (MS 170, MS180), and 1132 (MS 191T)
install same as above.
An oversize collar screw, part number 1115 664 2405, is available for alloy housings that have been stripped. The damaged hole will need to be drilled out to 8.5 mm (0.335” or letter drill Q) and rethreaded with a 10 mm by 1.5 pitch tap. Coat the threads with Red LOCKTITE 262, or equivalent, and install with the stud remover or use the double nut method. This collar screw is for the 3003 bar mount.