I like the NET translation of Romans 3:25 where 'propitiation' is replaced by 'mercy seat':
Romans 3:25-26
God publicly displayed him at his death as the mercy seat accessible through faith. This was to demonstrate his righteousness, because God in his forbearance had passed over the sins previously committed. This was also to demonstrate his righteousness in the present time, so that he would be just and the justifier of the one who lives because of Jesus faithfulness.
The following translation note is included:
33tn The word iJlasthvrion (Jilasthrion) may carry the general sense place of satisfaction, referring to the place where Gods wrath toward sin is satisfied. More likely, though, it refers specifically to the mercy seat, i.e., the covering of the ark where the blood was sprinkled in the OT ritual on the Day of Atonement (Yom Kippur). This term is used only one other time in the NT: Heb 9:5, where it is rendered mercy seat. There it describes the altar in the most holy place (holy of holies). Thus Paul is saying that God displayed Jesus as the mercy seat, the place where propitiation was accomplished. See N. S. L. Fryer, The Meaning and Translation of Hilasterion in Romans 3:25, EvQ 59 (1987): 99-116, who concludes the term is a neuter accusative substantive best translated mercy seat or propitiatory covering, and D. P. Bailey, Jesus As the Mercy Seat: The Semantics and Theology of Pauls Use of Hilasterion in Romans 3:25 (Ph.D. diss., University of Cambridge, 1999), who argues that this is a direct reference to the mercy seat which covered the ark of the covenant.
34tn The prepositional phrase diaV pivstew" (dia pistew") here modifies the noun iJlasthvrion (Jilasthrion). As such it forms a complete noun phrase and could be written as mercy-seat-accessible-through-faith to emphasize the singular idea. See Rom 1:4 for a similar construction. The word accessible is not in the Greek text but has been supplied to clarify the idea expressed by the prepositional phrase (cf. NRSV: effective through faith).