So, the "problem" is this: When i put the key into my 1999 GS, i find it hard to turn the key over. From steer lock to normal, and normal to on, i always have to jiggle the key up, down, left and right a bit before it seems to find the courage to turn. When it does turn, it isnt hard or something, it turns like a charm!
It has no problems on the tank cap lock, and the buddy release lock, whatsoever

I personally don't have to much of a problem with it, i've gotten the hang of it for a bit now, but this won't help me if i ever want to sell the bike, plus it's a bit annoying and jerky everytime i walk over to my bike, to get it off of steering lock, and into ignition on mode.

Is this a GS500 thing? or should a replacement lock solve this problem for me?

Also, i can pull the key from the ignition when its in on position, so it'll keep running. is that normal?

Not normal to be able to remove key that's for sure! .. would think that either your key or your ignition barrel is awry somehow! ..  seeing as the tank and seat lock work ok then the ignition barrel would be the culprit!   ...
Note on this though.  Different vehicles I have owned/ used have a minor situation... the ignition uses the full length of the key, but the doors/ glovebox might only use 80% of the length.... so. .

May be worth getting a locksmith to check your ignition barrel for worn springs/pins or just a small part of key is damaged? (at what $ though?) ..
Alternatively get a new ignition barrel,  coded or uncoded? and go from there... advantage of uncoded is you get it setup to accept your existing key,..  1 key to bother with! Or just put a coded one in and accept you may have to put a spot of paint/mark it. . To lessen the 'wrong Damn key!' Situ. . Lol

Wups forgot. . If it's the key teeth that are worn/damaged you may be able to contact Suzuki and get info on the 'original cut' of the key and then just get a key place to make you one! .. some cars you can do this and some not!

Or there could just be gunk waaaay down the bottom of the barrel that's stopping the key from seating fully by a tiny bit! ... maybe a squirt of brake cleaner in there?

Mine was like that, then it broke off in the ignition.  A locksmith cut me new keys, and they work properly.

It seems that worn out keys just do that, so try getting a new one cut.

Try a new key, but ask for a 2004 or newer key blank (or get one of the many variants from eBay). I believe the key from that vintage was shorter. The key mine came with was a copy, but displayed the same need to fiddled with to get into and out of each position. Having the key copied to the newer, larger blank solved that fiddle problem. Now it's easier turn and grasp with gloves, large hands, large cold hands or large cold gloved hands.

H O W E V E R - GET ANOTHER COPY WITH THE ORIGINAL SMALL BLANK.

Keep it on the same ring as the ignition key and use THAT one for opening the gas cap and releasing the seat.

Just a little safeguard to keep you from having to find out what it feels like to be stuck with a broke key in the cylinder...

I just put some motor oil on the key, stick it in and work it to all positions many times, repeat a few times, try that first.

regards
mech

I tried squirting down some WD40 down the lock. This used to work for me on mopeds i had with this problem, but to no avail this time.
I had a locksmith duplicate the keys for me, which gave me the same problem. I guess that;s to be expected when you duplicate a worn key.

However, i just found out that an ignition, tank cap, buddy lock and key will set me back 50 EU, so i think ill just do that then. Offcourse i'll be in touch with the suplier, to check if the lock i want tot order is OK in this aspect. it will be a secondhand lock afterall.