1993 LE Transmission

1993 Toyota Camry LE 4 cyl. 195000 miles
Today I put my car into drive and the transmission didnt engage. It behaved as if it was in neutral. About 3 seconds later, it engaged, and shifted normally. It shifts perfect, just like new. I was thinking the filter could be clogged. I dont know a whole lot about transmissions, so any help will be appreciated. Just want to tackle the problem so the transmission isn't fried.
Also, Transmission fluid is turning light brown, time for a change, but I'm afraid a change will trigger the problem, and I dont have the money for a rebuild. Could I get more life from it by it by changing it, or leaving it as-is? Also, the Lucas Transmission additives. Are they good or bad? Should I use it?

You should change the fluid. It is worse to leave the fluid in that has obviously lost the properties that make it tranny fluid, not to mention the debris in the fluid and filter. I can't say that additives will help, but if you have money, throw some of it away.

Like Joe said: Flush the tranny fluid - forget the additives.