I'd look at re-gluing the tape using contact adhesive, put plenty on both the tape and the tent, making sure you can force some of the glue into the seam. This what I did. Alternatively, if you find the tape has shrunk and won't fit exactly back into place, is to cut the tape. This may leave a small gap and you cut a strip from something waterproof the same width as the original tape and glue this over the gap.
To remove the mould I'd use 'mould killer' or something similar which I believe is nothing more than a weak bleach solution (it smells of chlorine) and follow this up with a scrubbing of mild detergent.
For waterproofing, I've been using 'Nikwax' Tent and Gear Solarproof (it comes in a spray bottle) starting with an initial coating along all the seams using a paint brush, followed up with an all over application with the spray and spreading it around with a sponge. I must admit however that my tent hasn't been really wet as most time there's only been a light shower or two when I've put it up.
Hope this helps.
replied on Sep 14, 2016