It’s hard to put a “Work Horse” label on an aircraft and not include all operations. In my personal experience, an 8-10 hour flight day or night was the norm. I recall this because we had a 25 hr Intermediate Inspection that would come due every 2-3 days. With that said along with high flight hour rates, we did not have wash racks that you find in today’s aviation, nor the time to wash aircraft. A big point on wreathing is that in later years, the birds did have the IR Suppressor (toilet Seat) installed, so the exhaust weathering was on the second 1/2 of the tailboom. If a IR Suppressor is not installed the exhaust trail starts at the dog house (exhaust cowling) and continues the leng of the boom getting lighter as you progress aft. The underside of the aircraft would get pretty dirty with the monsoons rains and unapproved landing areas. Mud was a big factor since with the mud trail was in and out of the aircraft during loading and unloading. The Dustoff aircraft were down in the jungle as much as any other mission birds; so the Dustoff birds got just as much as a beating as other hueys..
Hope this helps; good luck with your build.
On the bench...
1/35 Night Hawk low bird
1/48 Huey II