Cracked frame 2016 Trek Emonda
Bought this 2016 Emonda in mid 2017. There were no marks, scuffs, anything (it looked brand new), when I bought it 2nd hand. In late March 2019 I noticed cracks in frame (pictured) under seat pole, on both sides of frame. I'm perplexed how this has happened. No drops, no accidents, treated well etc. Has anyone else seen similar cracks on other Trek bikes? I found out later that the lifetime frame warranty only applies to 1st owner. Trek Australia have said they're not willing to do anything under warranty. They also refuse to assist in any other way such as providing store credit of any amount on purchase of new bike.
Is this acceptable that a 3 year old frame has cracked when there are no signs of damage to bike (apart from cracks)?
I have had this bike serviced several times at Trek previously. I've been told on each occasion that the bike is in good condition.
Finally, if the original owner did something that has now caused the cracks, would it take 2 years to be noticeable?