My 93 XJS antenna has I believe 4 sections, only the skinny top section and the fat lower section extends, the 2 middle sections don't extend. I actually prefer the look of a shorter antenna and reception seem to be fine but I would like to know what is causing this in case other sections decide not to extend. I did try lubing the antenna sections, but no go.

 

I know you have done it, but lack of lube is the root cause.

My X300, same. Got the wife to operate the radio whilst I "gently" coaxed the balance of the mast to extend. Wiped it with a "silicone spray" soaked rag, in an UPWARDS direction, so as to not push more muck into the joints. It took some time, and serious coaxing to get it sorted, but now (3 years on) still sweet.