I agree with dleo6466's advice, but would add that some heat applied to the reel seat will help loosen the old bond.

A hair dryer or heat gun works well, make sure you leave plenty of time to allow the heat to penetrate, it takes time. I would heat it for 5 minutes, rest it for 15 minutes and repeat. Too much heat, esp. with a high power heat gun could damage the wood.

Some folks have had good results using hot water. Boil a large pot of water, remove it from the stove and immerse the rod handle (wrapped in a plastic bag) and check every 15 minutes.

Just removing the butt cap might let you see what the problem is. The glue might have failed or perhaps some shim material such as masking tape has deteriorated. If it's just the tape failing you might be able to fix it in place by flooding the area with a thin penetrating super glue. Use 5 min. epoxy to replace the butt cap.

I like using 2 ton epoxy (longer working time) mixed with an epoxy filler to the consistancy of tooth paste. The filler makes the epoxy lighter, more flexible and enhances it's gap filling properties.

I try to fill the voids between my 1/2" masking tape shims so the epoxy paste holds the handle or reel seat in place, not the tape.

Mix the epoxy and filler about 50/50 in the corner of a plastic zip-lock bag and snip off the corner for a handy applicator. To fill the voids you will need about a golf ball size amount.

Epoxy filler such as 'Micro-Ballons' can be purchased at a hobby store that sells to the model aircraft crowd.

Use household vinegar to clean up any glue that squeezes out.