UTR - Very interesting to hear that Radar didn't have this Decath on radar. I've been given traffic advice in that area for a flock of birds heading my way so thought everything was on radar. Perhaps thick cloud will hide you and if that is the case, then that's really bad because perhaps anyone without a transponder possibly can't be seen for IFR traffic updates.
PS: I love hearing something like this:
Radar - VH-XXX, no observed IFR traffic for your descent. G'day.
XXX - Radar, do you have any VFR traffic for my descent?
Radar - VH-XXX, yeah sure, 1 at 2 o'clock, 1 at 12 o'clock and 1 at 11 O'clock, at your altitude. G'day.