Well the 10MHz oscillator for £2.98 from fleabay arrived today so i thought I'd give it a go. As per previous tests, it work well as an external reference as far as the jitter goes which disappeared when it was connected. So a cheap as chips xtal has less jitter than the DS4000 series internal timebase lol.
I've not heard back from Rigol eu yet, but I'll give it a few more days and then escalate it.
One saving grace though, as discussed earlier, if you start the scope and THEN connect the ext ref, it doesn't lock, you have to cycle the clockout/clockin. However, if the extref was set to clockin the last time you turned it off, it will lock. so.... if you have your ext ref always connected and the extref to clockin it does lock during boot up. Pity there's no indicator on the screen
I also tried different voltages for the ext clock and it actually works down to 100mV which is nice. Differing voltages from 100mV to 4V don't help the locking/jitter situation though.
Cheers
Steve