Spring AOP pointcut execution not working

I'm working on a Spring Boot project that uses Spring Cloud (io.awspring.cloud:spring-cloud-aws-dependencies:2.4.2) to produce and consume AWS SQS messages. I have several message producers and several message consumers, and all is working fine from that perspective.

I now have a cross cutting concern where I need to set a header on all messages being produced/sent; and to read that header on all messages being consumed (correlationId), and AOP seems like a good fit.

My aspect for handling (receiving) a message works fine:

    @Before("execution(* org.springframework.messaging.handler.invocation.AbstractMethodMessageHandler.handleMessage(..))")
    fun beforeHandleMessage(joinPoint: JoinPoint) {

The class and method that it is targeting is:

package org.springframework.messaging.handler.invocation;
...
public abstract class AbstractMethodMessageHandler<T>
        implements MessageHandler, ApplicationContextAware, InitializingBean {
...
    @Override
    public void handleMessage(Message<?> message) throws MessagingException {

As mentioned, this works great.

However, I can't get my pointcut for sending a message working. This is my aspect:

    @Before("execution(* org.springframework.messaging.support.AbstractMessageChannel.send(..))")
    // @Before("execution(* io.awspring.cloud.messaging.core.QueueMessageChannel.send(..))")
    fun beforeSendMessage(joinPoint: JoinPoint) {

And the class and method that I'm trying to target is this:

package org.springframework.messaging.support;
...
public abstract class AbstractMessageChannel implements MessageChannel, InterceptableChannel, BeanNameAware {
...
    @Override
    public final boolean send(Message<?> message) {

But it doesn't seem to work. I've also tried writing the pointcut to target the concrete implementation class (as commented out above), but that also does nothing.

I can't see what the difference is between my working pointcut for beforeHandleMessage and beforeSendMethod, other than the pointcut for beforeSendMethod is targeting a final method. Is that relevant?

Any pointers to get this working would be very much appreciated;
Thanks