Can someone enlighten me on this subject?

Some discussion perhaps? Personal experiences are most welcome.

Only by trying it yourself you can discover the power of a mantra. If you didn't have any Mantra Diksha(Mantra Initiation), you wouldn't have any power from your chant. It is symbolized by Shiva without Shakti. Shiva or Yang or masculine energy materialized in our dimension as doing, working, etc; whilst Shakti or Yin or feminine energy materialized as receiving. So, when you don't have Shakti, it means you cannot directly receive anything through any mantra. It doesn't mean nothing, because there would still be an effect, but so small--because even simply our thoughts or imaginations can produce results in physical world. If you'd like to try, you can pick any mantra that you like, use it to chant everyday--15-30 minutes is a good practice, and the more you chant, the faster your initiation would be. You don't have to search for any Guru 'cause your Guru would come when you're ready. For comparison, I chanted 5-10 hours a day before I finally receive my Diksha after about 2 years. My Diksha even came not "through" physical world as I expected, but through dream.
So, if you want to know or more precisely, feel the power of Mantra, you should try it. And I wish you luck with your endeavour!

is diksha the guru-disciple initiation?

you said your diksha came in the form of a dream? interesting.

i have been chanting several yrs, i wonder if i will have such breakthru....

Yes, Diksha is Guru-disciple initiation. But through my experience, I would recommend not to search or even pay for a Guru. A Guru-disciple relationship is not bound by anything physical, not even money, 'cause that relationship is a relationship of the heart. I'm also disagree with some who said that your Guru would speak with the language as yours. No, because a Guru would speak with the language of the heart with his/her disciple.
    When you have chanted for quite long time but still do not receive Diksha, do not despair. Everyone is different. I used to compare my spiritual training with others too, but I realized that it's useless. In Wicca, it is said that what you receive equals what you give. When you have to wait so long, there must be greater prize that you would receive.
    And for some reminder : when practicing Mantra--or I prefer to call it Mantra Yoga--you're also raising your Kundalini, even if you didn't receive Initiation. So you must beware of Kundalini syndrome, that is overload of energy. When you feel any discomfort, or even pain, you should stop your practice until the pain is gone. In my experience, I felt pain in my heart & in another occasion, it came as headache. The pain is different from ordinary illness. Like the pain in my heart, it was gone when I wake up in the morning, but would came back when I started my Japa again. For my headache, it was felt like there was water in my head. Those pains came before I received my Diksha.
    By the way, if you think that I'm faster than you in receiving Diksha, I have to 'paid so much' for it. I was in 'great darkness' that time. Someone put a curse upon me using a technique resembles Hoodoo & no one could even helped, whilst I lost all of my money for trying to found any.
    Those are some stories of mine. I hope it can encourage you in your spiritual jurney.
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Abu Ma'Shar (787-886) known in the west as Albumassar said in "Albumassar in Sadan"
asserted prayers would be answered when the Moon and Jupiter are in conjunction in the
head of the dragon.

Also, many traditions assert that the best time for particular activities such as Chanting etc.,
is dependant for efficacy on the Planetary Day and Planetary Hour. For example, prayer to
or through the influence of Jupiter or for Jupiter related activities or alleviation of Jupiter
related effects should be done on Jupiter hours and Jupiter Days. A waxing Moon ( increasing
in brightness ) is also important.

Mantras are available on the net and usually have a specific number of repetitions associated
with their evocation - for example the Mantra to the Sun is chanted 7000 times, Jupiter 19,000
times. These may involve fasting, sacrifice and other activities as appropriate.

An analysis of the natal chart including Dhasa's and Bhukti's with the current request can align
many forces to align as many favorable elements as possible to enable a request.