Question

퇴근하는 길에 헤어샵에 들를 거라서 조금 늦을지도 모르겠어요 -아/어서 cannot be affixed by the tense markers -았/었- and -겠-. However, it can be used with the -ㄴ/은/는/(으)ㄹ 것이- structure. When followed by -아/어서, the -것 (or -거) part becomes 것이어서, 거여서, 것이라서 or 거라서. Again, versions with -이라서 are more common.

Accepted Answer

I plan to stop by the barber's on my way home so I may be a little late

Front	퇴근하는 길에 헤어샵에 들를 거라서 조금 늦을지도 모르겠어요
Back	I plan to stop by the barber's on my way home so I may be a little late
Notes	-아/어서 cannot be affixed by the tense markers -았/었- and -겠-. However, it can be used with the -ㄴ/은/는/(으)ㄹ 것이- structure. When followed by -아/어서, the -것 (or -거) part becomes 것이어서, 거여서, 것이라서 or 거라서. Again, versions with -이라서 are more common.

I 퇴근하는 길에 헤어샵에 들를 거라서 조금 늦을지도