1981 KZ440: Oil filter removal?

[KZ440]

Hi. My bike has been sitting for 10 years. I am trying to change the oil and filter but can't get the filter out. The 17mm bolt is rounded, although a 6 sided socket can get a grip (a 12 point one slips). I have used a lever (approx 600mm) and an impact wrench but neither moves it, although there is not enough room for a proper swing with a hammer.

Any suggestions to help me move it? Thanks.

[FROSTY:Me]

Are you SURE you are removing the oil filter??
If you are 100% sure its the oil filter bolt then theres something reall wrong if you're using a 600mm bar and its still not budging.
Can you bring the bike to me to look at??

[p.dath]

Any signs of corrosion? How about spraying something like CRC on it and letting it soak in and then trying again.