VMS program to read/write simh .tap container files?

I have a TH4AA (a DLT-III drive, I believe) that's marked "Not TK50/70 Certified" - does it not really mean that, or am I just unlucky enough to have one of the DLT drives that's not backward compatible? And the real question is are the more modern DLT drives any more reliable at reading TK50s than the older drives? One problem is that the TK50 tapes don't seem to survive long term storage very well. Most of the old tapes I have leave copious amounts of gunk on the heads after even one pass thru the drive. In severe cases, the tape actually becomes stuck (glued!) to the head to the point where the drive motors aren't able to move it anymore. Then you have to disassemble the drive, unstick the tape, clean the tape path, reassemble everything, and then try to convince the drive to rewind and unload the tape for you. Speaking of which, does anybody know why a TK70/TZ30 drive, when you power it up and press the unload button, insists on spacing forward for ten or fifteen feet _before_ it'll finally start rewinding? Bob