Your V9 may suffer the indignity of my V7 III.
There is no way to check transmission fluid level except by draining, measuring and copying that volume for refilling. Of course you need to account for cling related temperatures, especially if the out-going oil is not hot. Otherwise the laws of diminishing returns always apply. Do sight ports scare the b'geesus out of Guzzi engineering. I believe the fill volume is 500cc, same as the V7 or by popular comments, 450cc's, in hot weather/hard rides. The caution regards venting and attendant mess, rear tire shine, etc. Good fortune, R3~