Depends on the MI's but they are not normally sealed on the inside. A lot of these issues arise because the tray isn't sealed to the wall before the door upstands are fitted.
You either seal outside or not at all depending on the tray type. If the tray an outside lip then no need to seal. If it hasn't then it will need sealed, yes. Usually outside to allow any water that may enter the wall frame to drain back out into the tray.
Is it leaking from under the metal trim, on a straight edged tray? If so then it needs sealed from the outside regardless. If it still leaks, as mentioned, look at the tile to tray seal.
No.1 culprit for leaking trays is behind the bottom heel of the screen wall profiles not being siliconed - it's the reason you should seal all round tray to wall 'before' tiling, as well as 'after'!
Always silicone outside profiles and around the outside of the base frame.
Never silicone inside the shower, doing so will trap water inside the profile and degrade silicone .
Depending on how good /steady you are! Put the silicone on Free hand to the profile/ glass, as if you smooth down with wet finger you"ll smear it everywhere and look terrible.
Then i use a silicone tool to clean up around the base making sure nothings been missed.
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