There are seasonal variations, but they are negligible. The biggest driver of seasonal variation on Earth is the 23 degree tilt. The Moon, however, with very little tilt compared to the Sun (1.54 degrees to the ecliptic), would have much smaller seasonal variations.
The biggest variation on the Moon's surface, as you pointed out, are the temperature swings between day and night. These diurnal variations dwarf any seasonal variations and make them unnoticeable, and improbable to measure.
It's important to also understand the importance of atmosphere for controlling these diurnal and seasonal variations. If the Earth had no atmosphere, it would experience violent temperature swings similar to that on the Moon, making it very difficult to measure the seasonal changes of even a 23 degree tilted body.
So, the negligible exosphere and small tilt of the Moon do not allow for seasonal variations that resemble those here on Earth.