Does this come from the specifications or the sticker on the back of the unit - these do not adhere particularly well so if it has peeled off you would measure the resistance of the one in the working speaker.
This model of speaker was quite prominent in the bass region. The bass units are paired 8066W8 wired in parallel - the 4 ohm impedance would make these more sensitive than the other drivers if these were 8 ohm units.
There are 5060SQ8's on offer on ebay - some pretty shabby examples and for silly money. There are specialists in speaker repair who could replace a voice coil for less money.
I have a vague feeling 5060W's are pretty much the same speaker minus the sub - enclosure.
I found the AD 5060 SQ8 (8 Ohm version).
PM me if you are interested.
alexanderfa is on the lookout for a replacement apparently an SQ4 version. I do have a couple of NOS SQ8's that I am planning to use in my next speaker project so my interest has been more as a spectator.