Changing the transmission fluid?
Many Rialta officionados agree at least every 20,000 miles the transmission fluid needs to be changed. If you are putting hard miles on (mtn. driving or hot temp. driving many choose to chg. every 10,000 miles or 12annually after a major trip). Many folks add a dipstick tube and dipstick. Though not readily available search a Calif. co. named Europarts and you should be able to come up with one. The transmissions need TLC so changing the fluid frequently makes sense.
98 RC Twin