Thanks for all the comments guys - much appreciated.
With regard to a spring loaded mechanism: There is no evidence, that a spring loaded latch was used; for example, there are no screw holes in the underside of the word above the top drawer, or near the back of the drawer. Nothing could be mounted behind the drawer, because the tambour door curves around behind it when the tambour is open. As near as I can tell, the only place any kind of spring might have been mounted is on the back corners of the top drawer. Having said that, I do recall having once seen some kind of mechanism where one push released a spring and another push locked it in place - I 'll have to do a web search on that.
Another comment on the use of DeckBrite: When I got the chest, it had a faint mildew smell. I was hoping the DeckBrite would help to get rid of it, and was a bit disappointed that I could still detect a faint smell after cleaning. However, after drying and refinishing the chest, I can no longer smell mildew, so maybe it did the job. I may try it on another old chest I have, as nothing else I have tried for removing mildew smell has worked.