The reason your forks are now soft is because they don't have oil in them.
your fork must be a oil pressure fork like most motorbike forks,
the springs are not the only thing that helps keep the fork up, inside a motorbike fork there is generally a open bath of oil around the coil springs and damping system, there is also a "Air Space"
There is normally a factory preset area of "air space" inside the fork,
how much air space there is, is dictated by the quantity of oil inside the fork.
When the fork compresses the oil moves upwards and compresses the air, the further the air is compressed the harder it resists the compression.
if you don't have enough oil in the fork, then the air space becomes so large that near bottom out the air isn't compressing enough to reduce or stop the fork from bottoming out.
There is 3 things that stop your fork from bottoming out,
1. Compressed Air Space
2. Your Damping System
3. Your Coil Spring
All of these things have a certain role to play in suspension,
the coil spring is more to do with getting a good sag and overall rate,
the damping provides a controlled action, both stopping the fork moving too quickly or too slowly in either direction, the Air Space compression works with the Compression Damping and the spring to make the fork feel firmer or softer, and help assist the coil spring and damping system in resisting bottom out.
The damping system alone cannot stop you bottoming out, it needs a combination of the three systems in place inside your fork.
In regards to your fork failing, the Oil seal is put under massive pressure, when the fork isn't compressed there is no real force on the seals, however at bottom out there is MASSIVE force from the air space being compressed, or in other words there being compressed air.
if you put too much oil inside the fork, then 3 things can happen, 1. you can bottom out on the oil before the fork reaches its full travel, 2. The Fork becomes too stiff, 3. The Fork seals Fail and explode oil and crap everywhere.
it's unlikely that your oil seal will continue to hold heavy oil pressure without blowing, the specification of how much oil you can use in your fork varys only by about 5-10ml per leg.
if you go too far either way, your fork will either bottom out, or blow seals.
that 5-10ml of oil can make a MASSIVE difference to the way your fork feels, in terms of spring rate and firmness.
I suggest you remove the fork legs from the bike (take off the wheel, the brakes ect, remove the legs from the clamps)
on the side that "isn't" blown, remove the top cap, slide out the spring, and tip the oil into a measuring cup, pump the insides of the fork until ALL the oil is out.
then remove the oil from the other leg, and fill both sides with the measured amount of oil from the right leg, with Fresh 5wt Dirt Bike fork oil.
after you have reassembled the fork, try it, if it rebounds tooo fast then you will need heavier oil, switch to 10wt, and try again. once you find the right rebound vs oil weight, then ride the fork, if it feels too soft and bottoms out easily, come back and add 5ml of oil to each leg. then ride again. you want to be able to use ALL of your travel (all but maybe 2-5mm) on big hits or landings, If you can't then you risk blowing the seals again, and it might not be so pretty next time.
when testing the rebound, make sure you compress the fork as deeply as you can, (push bloody hard) when it rebounds it should rebound quickly, but controlled. As in it should return to it's original position as fast as possible without feeling like it's pogoing or bouncy.
You may find the further you compress it the slower it rebounds, it's important to get he rebound right for deep compressions, you don't want to be going over stutters and after the 4th one you have no suspension left cause it can't rebound quickly enough.
Hope this helps.
Juls
