Impossible to switch to transparency unit Epson Perfection 1660 Photo (GT-8300)

Hello everyone,

I got an Epson 1660 Photo scanner (GT-8300 in some parts of the world) which used to work in both flatbed and transparency unit 'earlier'

Unluckily nowadays xsane no longer shows the option to switch from flatbed to transparency unit.

It's quite simply the switch which is missing. I'm running openSUSE Leap 15.6 / kernel 6.4.0-150600.23.30-default

It has already been discussed here, where in the end they told me to file a bug report
https://www.linux-club.de/forum/t/epson-perfection-1660-photo-in-xsane-umschalter-von-flatbed-auf-durchlicht-verschwunden.124711

I'm adding the following from there:

wolfi@localhost:~> scanimage -A
Output format is not set, using pnm as a default.

All options specific to device `epson2:libusb:001:005':
--mode Lineart|Gray|Color [Lineart]
Selects the scan mode (e.g., lineart, monochrome, or color).
--depth 8|12|14|16bit [inactive]
Number of bits per sample, typical values are 1 for "line-art" and 8
for multibit scans.
--halftoning None|Halftone A (Hard Tone)|Halftone B (Soft Tone)|Halftone C (Net Screen)|Dither A (4x4 Bayer)|Dither B (4x4 Spiral)|Di
ther C (4x4 Net Screen)|Dither D (8x4 Net Screen)|Text Enhanced Technology|Download pattern A|Download pattern B [Halftone A (Hard Tone)]
Selects the halftone.
--dropout None|Red|Green|Blue [None] [advanced]
Selects the dropout.
--brightness -4..3 [0]
Selects the brightness.
--sharpness -2..2 [0]

--gamma-correction Default|User defined|High density printing|Low density printing|High contrast printing [Default]
Selects the gamma correction value from a list of pre-defined devices
or the user defined table, which can be downloaded to the scanner
--color-correction None|Built in CCT profile|User defined CCT profile [Built in CCT profile] [advanced]
Sets the color correction table for the selected output device.
--resolution 50|60|72|75|80|90|100|120|133|144|150|160|175|180|200|216|240|266|300|320|350|360|400|480|600|720|800|900|1200|1600|1800
|2400|3200|6400|9600|12800dpi [25]
Sets the resolution of the scanned image.
--threshold 0..255 [128]
Select minimum-brightness to get a white point
--mirror[=(yes|no)] [no]
Mirror the image.
--auto-area-segmentation[=(yes|no)] [yes]
Enables different dithering modes in image and text areas
--red-gamma-table 0..255,... [inactive]
Gamma-correction table for the red band.
--green-gamma-table 0..255,... [inactive]
Gamma-correction table for the green band.
--blue-gamma-table 0..255,... [inactive]
Gamma-correction table for the blue band.
--wait-for-button[=(yes|no)] [no] [advanced]
After sending the scan command, wait until the button on the scanner
is pressed to actually start the scan process.
--cct-type Automatic|Reflective|Colour negatives|Monochrome negatives|Colour positives [inactive]
Color correction profile type
--cct-profile -2..2,... [advanced]
Color correction profile data
--preview[=(yes|no)] [no]
Request a preview-quality scan.
-l 0..215.9mm [0]
Top-left x position of scan area.
-t 0..297.18mm [0]
Top-left y position of scan area.
-x 0..215.9mm [215.9]
Width of scan-area.
-y 0..297.18mm [297.18]
Height of scan-area.
--autofocus[=(yes|no)] [no] [advanced]
Perform autofocus before scan
--focus 0..254 [64] [advanced]
Focus position for manual focus
--source Flatbed [inactive]
Selects the scan source (such as a document-feeder).
--auto-eject[=(yes|no)] [inactive]
Eject document after scanning
--film-type Positive Film|Negative Film|Positive Slide|Negative Slide [inactive]

--bay 1|2|3|4|5|6 [inactive]
Select bay to scan
--eject [inactive]
Eject the sheet in the ADF
--adf-mode Simplex|Duplex [inactive]
Selects the ADF mode (simplex/duplex)