you don't say what model and year you Hyundai is but I'm assuming that its a manual transmission so I'd begin by draining the oil and as it exits allow it pass through some paper towels to catch any debris
if you have a lot of pieces of metal in the oil then you know it may be more economic to start looking for a new / good used unit
If this doesn't help then next check the gear linkage for any worn bushes or pivots as any lost motion means reduced effort at the gearbox and replace as necessary. Ideally have your assistant move the gear lever with you watching the linkage and see if you can spot where there is any excessive play or lost motion.
If its a cable type linkage check along the cable lengths for any damage or signs of heavy wear / fretting, if you find any replace the cable. There may be some adjustment on the cable tension at the gearbox end (depending on the year) and the cable should be tensioned so there is a minimum of slack but not so its taught
Then check gearbox oil levels and if its not been changed in the last 20K miles then drain it off and fill with fresh. I can strongly recommend the use of Castrol Syntrans 75W90 (was called SMX-S) as I've known it help with shift issues on many manual gearboxes
If your gearbox is meant to use GL4 oil (the Syntrans is GL5) then use Redline MT90 instead
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