Had similar issue.
Caught it early, leaked twice.
Put up all new weather stripping around entire slide.
Still had a little water.
Went back and caulked all trim (see picture).
Worked great.
Been months now.
Went back and caulked all doors/panels just to be sure (hot water heater, refrigerator, outdoor shower, heater exhaust, etc.).
To find leak, used leveling system to angle camper with drivers side well above passengers side. Used a garden watering can and started at the top (top of slide, slide awning attachment, windows, etc.) and worked my way down. Wifey inside giving me feedback.
Appears water was coming through cracks between slide and trim. Gap so small couldn't see with naked eye. Water then went to L bracket on bottom running length of slide, and then, depending on how camper parked, went to one of the dual rack brackets, and the water followed that to the inside floor.
Hope this helps.
PS-live/camp in an area that averages 60 inches a year, so a big deal to get fixed.