Mobil 291 is now removed as an approved lubricant by Honeywell as it does strange things inside the engine that at the moment can not be explained.
To my knowledge, there's never been a 146 or an RJ lost to a mechanical fault attributed to a design fault. All losses have been associted with human error. I'd welocome ay other views.
The 507 has same max power rating as the 502 however its T/O perf is better due to additional supercharger section. Allegedly the 507H is a better engine than the 507F. ("H" suffix indicates a hydromechanical fuel control unit, "F" suffix indicates FADEC control) in terms of reliability.
BAE has, in my view, taken a very proactive and open response to all the 146 issues in my view and have handled them head on, and well. Pitch oscillation springs to mind especially, with undoubtedly the hardest thing being an admittance of the problem.