Oh good i'm glad its not just me who can't manage a good proportion of these multi connectors, there's definately a knack to them.

The Toyota ones usually come apart no bother, because (at least on full size 4x4's) most if not all of these connectors outside the dry passenger cell have been sprayed in some form of white grease before clipping together, i am not aware of any other maker who does this but happy to be informed otherwise.

If i need to disconnect one, nine times out of ten it's in an inaccessible place so can't see what you're doing, i usually try to find the same plug more conveniently sited on the car and learn the knack undoing that one a few times before going for the awkward mother, and yes upon reassembly a squirt of white grease goes in.

Yeh, I was thinking I might put Vaseline on it with a cotton bud, but a spray grease is probably better.

Vaseline is better as spray grease goes hard usually, vaseline should make it easier to split the connection if it need pulling apart again. its used a lot in electrical connections for computers/ sealing car battery terminals

I did have some contact cleaner in an aerosol, but in the year or so since I used it (on the indicator switches) the whole can has leaked away.

That makes it rather expensive so I'll use these alternatives if I possibly can. Vaseline has the advantage of being, AFAIK, universally available.