The damper tube may be OK but a 6DW4/6CJ3/6CK3/6CH3 is easy to find. I have too many. I scrapped many RCA's with bad flys over the years.
It also sounds as if the 2AV2 is shorted, if it pegs the tester meter
Have you monitored the DC voltage on the 6JE6 grid? Usually the more negative it is, the lower cathode current would be. There are several .033-.068? caps across the horz eff coil too, which could cause it not to "dip" properly.
I have been able to lower the current in all post-CTC11 RCA's (not sure why yours increases beyond 220) by switching to the high line voltage tap on the power transformer primary.