Either buy the fiatecuscan programme and an ELM327 reader and re calibrate your sele system, or find someone who can do it for you. its a useful bit of kit and enables you to make all sorts of tests and adjustments on the gearbox actuator. I do mine once a month and keep the clutch free play adjusted and i've had no real problems. Clunking into gear and harsh gear changes are often just the actuator out of sink. The oil is most probably sele oil, which is expensive. I drained mine nearly a year ago and replaced it with standard Dextron 3 ATF, with no problems. I'm unsure whether sele oil and ATF will mix, i'd say not. Top it up with sele oil and keep an eye on the level to rule out a leak (don't overfill as the oil will be chucked out the over flow and give a false leak).
The trouble with non alfa workshops is they don't understand the sele system and won't work on it, or guarantee work carried out if they do.
I thinks it's best to try to sort out any issues with the sele gearbox before it goes wrong. I have had them working fine then quickly go into tow truck mode, leaving you stranded.