84 300DT with 203,000 km.

My daily driver starts, idles and runs fine. I had an Indy do a valve adjustment about 24,000 km. ago. The maintenance manual recommend to do a valve adjustment every 24,000 km. - should I do it by the book? Or can it wait for awhile? What are some of the symptoms that would indicate an overdue valve adjustment?

I plan to DIY the next time, after reading many threads about it here, but haven't got around to acquiring the special tools (i.e., bent 14" open wrenches and spring holder) required to make the job easier.

Thank you for your time.