Alpine V12 issues

Hi I have an MRV1507 with output issues on the bench,

the amp powers up and idle's fine,
with the input switch set to 1+2 mode it plays clean audio on both channels.

with the input switch set to stereo mode it only plays audio on the right channel and very low on the left, there's very low audio bridged.
Idle becomes erratic on bridged mode.

with the switch set to mono there's very low audio

I've already checked the amplifier board for dry joints and run solder on any suspect joints with no change.

any support with this appreciated
I drowned the switches in deoxit and switched them hundreds of times, stripped and cleaned the eq and gain pots with deoxit and managed to get all the functions back except left channel in stereo mode.

I had a spares MRVF400 with the same 3 way switch so I swapped it out with the input mode switch and thoroughly deoxit cleaned it the same as the others, I still don't have the left channel on stereo mode?

I noticed one of the vias came away from the board when I desoldered the original switch, it doesn't appear to be connected to anywhere as I can't see any traces, could it be a multi layered circuit board and am I missing a connection?

I know this is a waste of time typing this but I'd suggest an older CRT based scope due to display quality.

Buy what's available in your budget. I don't have any suggestions for someone buying an LCD based scope.

If you can work without the fancy digital readouts (few getting into this can) I'd recommend an old Tektronix 465B or many of the older 2200 series Tek scopes. Hitachi, Kenwood, BK precision all make very usable scopes and can often be purchased for about $150 used.

If you're going to buy off of ebay, email me the scopes that you're interested in.

As a minimum, you should only consider scopes that have a sharp, bright trance and those who have a locked waveform on the display. If you can find something locally that you can try before buying, that's a bonus.

Probes are dirt cheap. The ones you can buy on ebay for $5 each 4/$20 work perfectly fine for car audio.