Dried Coolant stains under passenger side of the dashboard. Is this a problem?

Heater Core, big job, but can be done at home.

Dried Coolant stains under passenger side of the dashboard. Is this a problem?

Yes.
Its not supposed to be there.
Your heater core o-rings and/or core is leaking. Meaning also, it may be leaking onto your ECU. Get it fixed, or at least bypassed (temporarily), ASAP.
Dash-out job to replace the replace the core, o-rings and the pipes. If its just the o-rings leaking, many just replace the o-rings and pipes, but I'd recommend replacing the core too (but thats just me), saves pulling out the dash a second time if the core leaks down the track.

Heater Core, big job, but can be done at home.

Thank you for your advice - much appreciated. Regards

Thank you for your advice - much appreciated. Regards

Yes.
Its not supposed to be there.
Your heater core o-rings and/or core is leaking. Meaning also, it may be leaking onto your ECU. Get it fixed, or at least bypassed (temporarily), ASAP.
Dash-out job to replace the replace the core, o-rings and the pipes. If its just the o-rings leaking, many just replace the o-rings and pipes, but I'd recommend replacing the core too (but thats just me), saves pulling out the dash a second time if the core leaks down the track.

Thank you for your advice - much appreciated. Regards