Valmiki Ramayana, Balakanda, ChaturVimsha sarga, verses 8-9:
Mansarovar is on Mt.Kailasa, and from Manasa sarovar flows a river close to Ayodhyapuri. Because this has originated from a lake, saraH, this is known as Sarayu. And because it flows from Brahma's Lake it is a merited river.
The current Sarayu river looks like it comes from Rakshastal and not from manasa sarovar.
Also according to Matsyapurana, adhay 121, shlok 14-17:
"Sarayu river flows west from Mansarovar"
But the current sarayu river flows south from Rakshastal. So if this is the case, how can we say that the current Ayodhya is real? and where is Ayodhya?
Note: I do not wish to offend anyone regarding my question. Our current thirthas are as holy regardless of their authenticity and I respect their location. Being a Hindu, I would never disrespect any thirth just because they do not match with shastras. Many thirthas have changed locations and this is why I try to find their original location. Sorry if I have offended anybody.