Issues with engaging gears is often the shifter cables, there is an adjuster in the cabin that can be moved to improve gear engagement to compensate for cable stretch etc. I have never heard of anyone needing to replace their syncros in these gearboxes to date, I hope it want too expensive.
http://www.ozmpsclub.com/forum/drive...ne-tuning.html
The turning noise is the infamous woong noise, it occurs at low speed, high angle turns (i.e U turn), it is the LSD doing its job and is totally harmless, you can probably hear it more now as your mechanic has used a different gearbox oil, you can either live with it, or find a quieter oil.
http://www.ozmpsclub.com/forum/drive...il-thread.html
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