Ukraine

It also depends how much they are willing to donate/sell/lease

In addition to the comments already posted, they had strategic reasons to withhold support as well. While Russia doesn't pose a serious military or economic threat to RoK directly they could cause real problems. Part of the defensive advantage they have held against the North is a decade or three of technology lead. While joking about the actual effectiveness of Russian hardware is fun, large scale tech transfer to North Korea would change the strategic balance on the peninsula, RoK has pretty clearly sought to avoid that by limiting aid to Ukraine to non lethal items.

The more Russia barters with the North though, the less likely RoK will see it that the transfer isn't taking place anyways. Russia is gambling for short term help and risking a major new source of munitions and hardware for their adversaries.

They have a constitutional ban on supplying weapons to countries at war. This is not a Ukraine thing specifically but a broader thing that was put in place long ago. The current geopolitical climate if forcing the south to re-evaluate their law... Which is good... I guess... A shame it's nessecary.

On the other hand if they make their MIC go bbbbbrrrrr creating 155 shells they have the ability to rotate out their stocks for fresh munitions while helping Ukraine and making bank.

They also have some top tier mine clearing and breaching machines. Their military is actually built for this kind of conflict.. long drawn out artillery slugfest.

They’re trying not to overtly antagonize the North, who have a SHITLOAD of artillery trained on Seoul. Like, thousands and thousands of artillery tubes.

But this is now the North doing the antagonizing..The north is failing to realize that that whole antagonization thing cuts both ways.

They've been circumventing their lethal munitions ban by issuing arms to the US, which then supplies the exact same number of munitions to Ukraine. It's escalation posturing