[X(]WARNING: newbie Q!!

I have a OFNA LX pro that has about 4-6mm of left/right steering slop
and i guess whats causing it is the 1.5-2mm gap between the spacers and bellcranks.

should i put another washer/spacer thingy between them to fill in the gap or leave it?

You should simply replace the worn or missing parts.

Could it be that your entiresteering linkage is worn out, or is it that you have a stripped Hitec servo in there.