if it is too hot to touch, then it is too hot. we use a Maxtrac for a link TX for paging, it is keyed up probably close to 18 hours in a 24 hours period. i have 2 fans on the heatsink and 1 CPU fan on the final, it has run like this for 6-7 years and never had an issue.
how long are you keeping it keyed at a time and how much break between keyups?