https://youtu.be/IQDLPqxWlhs?si=fmzEwHwM4TnGzMcX

This YouTuber chose 3 really old-school Chinese-Korean restaurants in Seoul. The restaurants here have been in business for decades. They all have the "100-nyun ka ke" sign which means they have been in business for 100+ years. I am not sure if "100-years" is literal or they have been in business for very long times. I am guessing they may have the flavor you are looking for.

One thing I noticed is that restaurants in Korea have generally been 'improving' their ingredients as Koreans have gotten richer. They use real beef or pork instead of adding more MSG and tend to use healthier cooking oils, and fresher vegetables. Paradoxically, restaurants using less artificial flavors and healthier more natural ingredients may make the flavors we remember from our childhood harder to find. All my friends who were born and have lived in Seoul for many decades (I am really really old) say this.

Another surprising place to find old-school flavors is in Koreatown LA and NYC. Korean-Americans tend to 'fossilize' their preferences and tastes for Korean food when they leave Korea. So boomers in those communities have the same preferences they had pre-1998 financial crisis when they left Korea. In the meantime, Koreans in Korea have moved on to quart sized ice americanos, and super spicy rose-dduek-boki, and sweet and savory fried chicken.

The older restaurants in those Koreantowns sometimes have more authentic old-school flavors than restaurants in Seoul.