Do not use clear silicon on metal painted surfaces! Use adhesive caulk or some other sealer that is paint friendly. Bad place for screwing, make sure you use stainless hardware and seal it well, that's already a problem spot in a lot of early Zs I have seen around the southeast. It would be better to use one of the screws in the cabin nissan already has in place. They did that so as not to have a hole in the bottom of the sump. Not trying to bust your balls, but would hate to see you have to pull all that out a year or so down the road because its leaking and or rusting out.