I remember one just one of my treasured books 1955 copy of " the teachings of a compassionate Buddha" where I read that the Lord had a morbid fascination with death ..suffering etc and inquiring of death ( possibly a force //entity within)he gained insight into a possible way out of suffering ..rebirth etc pls let me know if this is true ? For example there is reference made to countless past lives of the Buddha by him so I guess he was able to tap into his own death.
While living in the palace, Prince Gotama realised he would die (read Sukhamala Sutta), which resulted in him losing intoxication with the ordinary life of pursuing transient pleasures, which he also saw caused anguish & addiction in people and brought little happiness & much disappointment (read Magandiya Sutta).
In other words, Gotama did not directly or actively inquire into death to gain enlightenment because death was an established fact to him. The 'morbidity' referred to is 'suffering' & Gautama's inquiry was always into suffering.
Therefore, when inquiring into suffering, Gotama inquired into Dependent Origination (read Maha Sakyamuni Gotamo Sutta). Gotama asked: "Why do beings suffer?" and answered: "Beings suffer due to aging & death", i.e, "loss'. Then Gotama asked: "Why do beings suffer due to aging & death?". His answer was "birth". Why does birth occur? Due to becoming & attachment, etc.
As for his countless "past lives" and also the word "reborn" (in SN 12.10, above), these are just mistranslations of the respective Pali words "pubbe nivāsa" and "uppajjati". For example, this translation of SN 22.79 correctly does not use the words "past lives". Instead, it uses "past abodes".
Everything above points to something called "birth" ("jati") as being the main problem the Buddha identified. After his enlightenment, the Buddha's 1st words were:
153. Through many a birth (jati) in samsara have I wandered in vain, seeking the builder of this house (gaha). Repeated birth is indeed suffering!
154. O house-builder, you are seen! You will not build this house again. For your rafters are broken and your ridgepole shattered. My mind has reached the Unconditioned; I have attained the destruction of craving
What "birth" ('jati') actually means will depend on your personal study, practise & realisation.
The Haliddakani Sutta may possibly provide some insight into what the Buddha meant by "abodes/homes/fixations" ('nivāsa'/nivesā) and "house/home" ('gaha').