F355 gearchange problems

I've had a 355 now for only 5 months and reckon it's a brilliant car, with one on-going problem, the gearshift. Does anyone have any ideas as to what may be the best way to improve the change? I'll run through what I've done so far.

Car delivered end August '06. Gearchange fine apart from poor 1st to 2nd change when cold. Thought this was standard after reading previous forum posts.

At the end of November I noticed poor 2nd to 3rd change when hot (feels like bulking). This is intermittent and only happens when revs are, say, above 5000rpm. The down change from 4th to 3rd is OK every time, no matter what revs. I can change up 1st through to 4th, accelerate up to about 3500rpm in 4th, release the clutch and change down to 3rd and down to 2nd (clutch still released) with no problem but when I change from 2nd to 3rd again (clutch still released) the gear will bulk, but not every time.

I've tried Redline 75w/90 (by mistake) and this made matters worse for all the gears (too slippery for the syncros). I now have Redline 75w/90 NS and there didn't appear to be any improvement over the original oil (Shell pressumably as car bought from Ferrari here in the UK) so I checked the gearchange adjustment.

The fore/aft adjustment seems to be by means of a threaded rod at the 'box end of the selector rod and I didn't think this was the cause of my fault so left that alone. I thought that perhaps the problem would be in the lateral movement of the lever which is adjustable after loosening 3 5mm allen headed screws. I selected 3rd gear, loosened the screws, and adjusted the selector rod to a point midway through its total free-play movement (this was an adjustment of about 2mm over the original setting). Now, after a cold start, the change to 2nd is much improved. When hot, the 3rd selection is alot smoother but still bulks occassionally. I reckon the adjustment made things better but it could be the Redline NS now doing its best after the previous oil has worn off the syncros.

What I can't understand is why the problem is intermittent. I've been in the motor trade here as a mechanic for 20 years now and stripped countless gearboxes. From experience, a bad syncro is a bad syncro and will always bulk especially at high speed changes and more so when hot.

Is there anything else that could cause the problem apart from an internal fault. I have a Ferrari Power Train warranty which covers the 'box but would rather try anything else before using the warranty as I dont want the car out of my hands if I can help it (it took the main dealer 3 weeks to do the belt service/clutch/sort the aircon).