just googled it!
10w40 is the thickness
API type is the quality (starting SA - best then SB, SC, SD..... etc)
Just gunna top up with this and then do a full change at the weekend with the propper stuff!
Thanks CMSMJ1 for all the advice.
I will keep posted if all goes well.
Thanks.

cool - aye, your bike is old so takes older referenced oils - newer stuff is good.

hope it gets sorted