The Michigan Interstate has one engine in particular that has had this journey. MCIS 4050 (EMD SD40-2 snoot Kato early) came from the former Santa Fe in the nineties when the railroad was shopping for mainline power.
Since coming on roster the engine had suffered a bent frame which required rebuild on a mid-production Kato frame with truck hardwiring. Most recently the unit received two new trucks from EGS Rail Services out of Kansas that were installed in house at the Mt. Pleasant shop. Finding trucks without parting out another engine is tough. While in the shops the engine also received a new microprocessor (Tsunami KT-1000 EMD645 sound decoder) which I have been very impressed with. This week shop forces will had the air conditioners and snow plow back.
Crews have dubbed this unit "Old Glory" as it looks tired, been through rough times, but continues to be reliable and prevail in mainline service.