Inside SDG1000 there is also place for better reference but it need (afaik) also modified FW from Siglent.
I have installed the latest firmware
Regards
Latest firmware is nothing to do this what I told.
I told, there is place for better freq reference (OCXO). There is allready place for it on the board but it need special FW also what support it. (Time ago Siglent tell me this)
If want install this special option it need instructions from Siglent how to do.
But if just change original default oscillator (and this is now case) to new one it can of course do.
I
believe it is now out of limits
but your method do not proof it. You have measured it by undefined accuracy. If one DSO have around what also your counter, it do not really proof so much.
For real
proof if siglent is out of specs or not and how much it is out of specs you need least +-10ppm true trusted abs accuracy or far better. (oh well it is easy get and perhaps your counter is inside this but this can not be sure with this information what is now.
If it really after trusted measurments is >400ppm off, it is absolutely too much = fail.
If there is warranty, contact first seller what to do.
If seller is just only carton shipper then contact Siglent and ask help for get this back to normal working state.