Vintage Synth Repair

Hi folks!

My Polysix after battery leakage had the typical symtomps you might
expect.

After having cleaned & resoldered the guts everything's fine apart 
from
the memory;
I create a patch, I press WRITE, I choose the location. Seems OK. But
just click another patch, then come back to the one I just saved - and
it's not there. A new 3.6V battery has been installed, but it is not
the matter of battery, beacause we are talking about doing this when
the synth is still operatnig, being plugged, so it has all the power
needed all the time.

I'm inclined to think the TC5514 S-RAM chip is the culprit, because 
all
the chips keep voltage of 5V whereas this one has just 4V.

What do you think ? What replacement part for TC5514 should I look 
for?
I've heard about Intersil HM6514 and Nec uPD444c (D444C-6514) but are
these really the only ones? I came across some chips with 'similar'
characteristics and I really would like to avoid importing the above
mentioned ICs.

I'm not a tech, but a tech's opinion would be greatly appreciated and
helpful.

cheers
aero