993 Tip gearbox - incorrect oil fill by OPC - advice sought

[Helgathe993Targa]

Dear TIPEC colleagues.

My 993 recently had its 30k mile service at an OPC.

On the way back the gear box started clunking and jolting. Returning it to them they inspected and after some days told me that they had put too little oil into the gearbox but it had now been topped by by 0.5 Litre and all was well.

I have asked if there can be any long term damage - I drove the car less than 30 miles - and they have assured me there will not. Of course a cynic would say "they would say that".

I would appreciate any informed comments or past experiences. Thank you