Build-up on a badly designed antenna can have severe effects!
The diameter of the most sensitive part of the antenna, the tank seal, is inversely
proportional to the transmitter frequency. This means that especially high-frequency
transmitters are sensitive to dirt and condensation since even a small amount of
particles can clog the tank seal.

A clogged tank seal will in the best case reduce the measurement margins and accuracy.
In the worst case it can make the transmitter lose the signal. Maintenance may be required
on a regular basis.