If you want a job doing right do it your bloody self !! I let a friend do an oil & filter change on my 97 diesel Astravan but now notice a few drops of oil leaking from around the oil filter o-seal. Thinking it was perhaps a touch loose I went to tweak it up slightly but couldn't tighten it anymore & didn't want to use excessive force. I think it's been put on too tight as I needed a filter wrench & a lot of effort to slacken in off. I loosened it enough to smear a bit of oil around the o-ring and try re-tighten to the correct tightness but there's still a bit of seepage so I think the o-ring has been crushed / damaged.
I don't mind fitting a new filter but just want to know if it's do-able without losing too much oil or will the fresh new oil in the sump need to be drained? wasn't sure if there's some kind of one way valve in the filter housing to stop it flowing back out?