The red outlane stays open the entire time.
The gate should be closed like Mk1Mod0's at the start of the game to make two outlanes and open once a "T or "U" upper rollover is completed to create two inlanes. It resets once the outer inlane has been rolled over and you have to rollover the T or U again to open it back up.
There should be two nails there that restrict the gates movement underneath the two wireforms. (Inlanes.)

Playing Future Spa with THREE left inlanes is cheating, which means no boob shower for you Troutfarm!

Future Spa pro tip:
Use blue incandescents behind the diffused logo to give it a richer; more sparkle-y zazz.

*Future Spa Police megaphone*
Step away from the technicolor LED bin sir! Drop those purple passions and put your hands on your head. What you are doing is a crime against pinmanity...

THIS is colorbombing done right...

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Most of the time the diffuser just falls off due to the age of the game and is either quietly sitting in the head, or the bottom cab, buried under old bulbs, rubber, coil dust, etc...

Clean it off, double-sided tape it and you're good to go for another 38 years.

No worries then, seems like Brich has found a suitable replacement so you should be good to go.
eBay has similar stuff available if and when he runs out.
Googling "transparent holographic film" will also give you a bunch of options to use.