Mine was 200 kilometers like brand new. Then one day rain poured on my bike while it was parked outside, without cover. 30 minute rain. Then, without letting it dry (just after an hour) i rode the bike home, some 12 kilometers. The next morning I saw it had formed in the shape of my butt.
Wouldn't recommend this method - i try to keep my leather seat away from rain, but it did work.
Proofhide was put on it when it was new and will be re-applied this autumn.