9.9 newtons meter = 7.30186528 foot pounds according to Google.
That's not a lot of force, you'd tighten the lug nuts on a compact car to about 75 foot pounds, by comparison. So...seven foot pounds would be "use a small short wrench and a limp wrist or ask a four year old to do it". Or hold your hand right over the bolt--not at the end of the handle--and tighten it about as much as the lid of a jelly jar.
(Well then again, if you buy a torque wrench they're not very expensive these days, and last a lifetime if you treat them right.)
If the one came that loose, it might just pay to buy whatever gaskets are needed, remove and retorque the entire cover so you know they are ALL seated properly. The copper tubing should have enough flex in it to allow that as long as you move gently. If it doesn't--then it was about to fail anyway. Copper work-hardens, better to fail at the dock than under way.