The red crap is to stop rust I would think.
There are putties on the market that will seal a hole and last a lifetime but a seam can be a hole other problem, the leak can just keep growing over time or it may never grow at all.
Sealing the tank from the inside is a proven fix if you follow the instruction to the letter.
Now the decision is do you have the time, the place and the skills required to seal the tank.
Then you would need to look at the cost, tank sealer and your time verse a replacement tank.
Lets face it that tank has seen better days.....
Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
Out of my depth in a puddle.
Live life on the edge you will see more that way.
Ridding a motorcycle keeps things in balance.
At the end of each trail and at the end of each day history is made.