broken locking levers on instrument cluster
 

Any idea if or how they're replaceable?

What do you mean?

One of the three wiring plug connectors is loose on the backside of my instrument cluster because the two little plastic locking tabs are broken off

Oh! well unless someone else knows better (and I hope they do) I would say they are not replaceable.

I would try and work out another way of securing it.

You would either have to de-pin the connector or source a connector with a length of wiring and cut your wiring and connector and solder the new connector with wiring into your harness. Or replace your harness... Not really a lot of options there..

Can't see what it looks like, but could you put a small cable zip tie, or possibly a wire around the socket and the plug?

The connector has little arms on each end of the connector that "cam" into a locking position as the connector is pushed into position. When the connector is to be removed, the arms are lifted as the connector is removed and move to an "open" position, ready to be pushed into the lock position when the connector is re-inserted. It's a great design, but due to it's location that's subject to plastic aging from heat and time and misunderstanding from technicians on how to remove them, they commonly fail.

OK, so slide a couple of some fine monofilament fishing lines under the socket, insert the plug and tie a knot to hold them together. BTDT.

Thanks will give that a try