I rebooted and checked to find it is idle at 98C. I need this thermal paste. Is there one that can be recommended?
The thermal paste needs to be changed only in one case - if you remove the processor and want to put it back later or replace it with another one. Then there is usually a situation where the old paste has hardened and there is generally too little of it.
Only then will you need a new paste. Just like that, it never needs to be replaced or changed.
But of course you may renew it, but it is quite likely that it will not give any result, that is, it will not change anything. Only proper mechanical cleaning (all dust and grease should be removed regurarely) and , as well as removal of non-selection and any other junk (including junk files and redudant registry keys), will most likely help.
The normal temperature of this processor is 72C - 75C, briefly allowed up to 90C.
But on idle it must be somewhere around 48C - 54C depending what background proccesses a running.